Napoleon Bonaparte (15 August 1769 – 5 May 1821), was a military and political leader of France and Emperor of the French as Napoleon I, whose actions shaped European politics in the early 19th century.

Born in Corsica and trained as an artillery officer in mainland France, Bonaparte rose to prominence under the First French Republic and led successful campaigns against the First and Second Coalitions arrayed against France. In 1799, he staged a coup d'état and installed himself as First Consul; five years later the French Senate proclaimed him Emperor. In the first decade of the nineteenth century, the French Empire under Napoleon engaged in a series of conflicts — the Napoleonic Wars — involving every major European power. After a streak of victories, France secured a dominant position in continental Europe and Napoleon maintained the French sphere of influence through the formation of extensive alliances and the appointment of friends and family members to rule other European countries as French client states. The French invasion of Russia in 1812 marked a turning point in Napoleon's fortunes. His Grande Armée was badly damaged in the campaign and never fully recovered. In 1813, the Sixth Coalition defeated his forces at Leipzig; the following year the Coalition invaded France, forced Napoleon to abdicate and exiled him to the island of Elba. Less than a year later, he escaped Elba and returned to power, but was defeated at the Battle of Waterloo in June 1815. Napoleon spent the last six years of his life under British supervision on the island of Saint Helena. An autopsy concluded he died of stomach cancer, though Sten Forshufvud and other scientists have since conjectured that he was poisoned with arsenic. Napoleon's campaigns are studied at military academies the world over. While considered a tyrant by his opponents, he is also remembered for the establishment of the Napoleonic code, which laid the administrative and judicial foundations for much of Western Europe.

Napoleon Bonaparte was born the second of eight children, in Casa Buonaparte in the town of Ajaccio, Corsica, on 15 August 1769, one year after the island was transferred to France by the Republic of Genoa. He was initially named Napoleone di Buonaparte, acquiring his first name from an uncle who had been killed fighting the French, but later adopted the more French-sounding Napoléon Bonaparte. The Corsican Buonapartes originated from minor Italian nobility, who had come to Corsica in the 16th century. His father Nobile Carlo Buonaparte, an attorney, was named Corsica's representative to the court of Louis XVI in 1777. The dominant influence of Napoleon's childhood was his mother, Maria Letizia Ramolino, whose firm discipline restrained a rambunctious child. He had an elder brother, Joseph; and younger siblings Lucien, Elisa, Louis, Pauline, Caroline and Jérôme. Napoleon was baptised as a Catholic just before his second birthday, on 21 July 1771 at Ajaccio Cathedral. Napoleon's noble, moderately affluent background and family connections afforded him greater opportunities to study than were available to a typical Corsican of the time. In January 1779, Napoleon was enrolled at a religious school in Autun, mainland France, to learn French, and in May he was admitted to a military academy at Brienne-le-Château. He spoke with a marked Corsican accent and never learned to spell properly. Napoleon was teased by other students for his accent and applied himself to study. An examiner observed that Napoleon "has always been distinguished for his application in mathematics. He is fairly well acquainted with history and geography... This boy would make an excellent sailor." On completion of his studies at Brienne in 1784, Napoleon was admitted to the elite École Militaire in Paris; this ended his naval ambition, which had led him to consider an application to the British Royal Navy. Instead, he trained to become an artillery officer and, when his father's death reduced his income, was forced to complete the two-year course in one year. He was examined by the famed scientist Pierre-Simon Laplace, whom Napoleon later appointed to the Senate.

Upon graduating in September 1785, Bonaparte was commissioned a second lieutenant in La Fère artillery regiment. He served on garrison duty in Valence, Drôme and Auxonne until after the outbreak of the French Revolution in 1789, though he took nearly two years of leave in Corsica and Paris during this period. A fervent Corsican nationalist, Bonaparte wrote to the Corsican leader Pasquale Paoli in May 1789: "As the nation was perishing I was born. Thirty thousand Frenchmen were vomited on to our shores, drowning the throne of liberty in waves of blood. Such was the odious sight which was the first to strike me." He spent the early years of the Revolution in Corsica, fighting in a complex three-way struggle between royalists, revolutionaries, and Corsican nationalists. He supported the revolutionary Jacobin faction, gained the rank of Lieutenant Colonel and command over a battalion of volunteers. After he had exceeded his leave of absence and led a riot against a French army in Corsica, he was somehow able to convince military authorities in Paris to promote him to Captain in July 1792. He returned to Corsica once again, and came into conflict with Paoli, who had decided to split with France and sabotage a French assault on the Sardinian island of La Maddalena, where Bonaparte was one of the expedition leaders. Bonaparte and his family had to flee to the French mainland in June 1793 because of the split with Paoli. In July 1793, he published a pro-republican pamphlet, Le Souper de Beaucaire (Supper at Beaucaire), which gained him the admiration and support of Augustin Robespierre, younger brother of the Revolutionary leader Maximilien Robespierre. With the help of fellow Corsican Antoine Christophe Saliceti, Bonaparte was appointed artillery commander of the republican forces at the siege of Toulon. The city had risen against the republican government and was occupied by British troops. He adopted a plan to capture a hill placing that would allow republican guns to dominate the city's harbour and force the British ships to evacuate. The assault on the position, during which Bonaparte was wounded in the thigh, led to the capture of the city and his promotion to Brigadier General. His actions brought him to the attention of the Committee of Public Safety and he was given command of the artillery arm of France's Army of Italy. He became engaged to Désirée Clary, whose sister, Julie Clary, married Bonaparte's elder brother Joseph in 1794. The Clarys were a wealthy merchant family from Marseilles.

Following the fall of the Robespierres in the July 1794 Thermidorian Reaction, Bonaparte was put under house arrest in August 1794 for his association with the brothers. Although he was released after only ten days, he remained out of favour. In April 1795, he was assigned to the Army of the West, which was engaged in the War in the Vendée — a civil war and royalist counter-revolution in France's Vendée region. As an infantry command, it was a demotion from artillery general, and he pleaded poor health to avoid the posting. He was moved to the Bureau of Topography of the Committee of Public Safety and sought, unsuccessfully, to be transferred to Constantinople (officially renamed Istanbul on 28 March 1930) in order to offer his services to the Sultan. During this period he wrote a romantic novella, Clisson et Eugénie, about a soldier and his lover, in a clear parallel to Bonaparte's own relationship with Désirée. On 15 September Bonaparte was removed from the list of generals in regular service, with the reason given being his refusal to serve in the Vendée campaign. He now faced a difficult financial situation and further reduced career prospects. On 3 October, royalists in Paris declared a rebellion against the National Convention after they were excluded from a new government, the Directory. One of the leaders of the Thermidorian Reaction, Paul Barras, knew of Bonaparte's military exploits at Toulon and gave him command of the improvised forces in defence of the Convention in the Tuileries Palace. Bonaparte had witnessed the massacre of the King's Swiss Guard there three years earlier and realised artillery would be the key to its defence. He ordered a young cavalry officer, Joachim Murat, to seize large cannons and used them to repel the attackers on 5 October 1795 — 13 Vendémiaire An IV in the French Republican Calendar. 1,400 royalists died and the rest fled. He had cleared the streets with "a whiff of grapeshot", according to the 19th-century historian Thomas Carlyle in The French Revolution: A History. The defeat of the Royalist insurrection extinguished the threat to the Convention and earned Bonaparte sudden fame, wealth, and the patronage of the new Directory; Murat would become his brother-in-law and one of his generals. Bonaparte was promoted to Commander of the Interior and given command of the Army of Italy. Within weeks he was romantically attached to Barras's former mistress, Joséphine de Beauharnais, whom he married on 9 March 1796 after he had broken off his engagement to Désirée Clary.

Two days after the marriage, Bonaparte left Paris to take command of the Army of Italy and led it on a successful invasion of Italy. At the Battle of Lodi he defeated Austrian forces, then drove them out of Lombardy. He was defeated at Caldiero by Austrian reinforcements, led by József Alvinczi, though Bonaparte regained the initiative at the crucial Battle of the Bridge of Arcole and proceeded to subdue the Papal States. Bonaparte argued against the wishes of Directory atheists to march on Rome and dethrone the Pope as he reasoned this would create a power vacuum which would be exploited by the Kingdom of Naples. Instead, in March 1797, Bonaparte led his army into Austria and forced it to negotiate peace. The Treaty of Leoben gave France control of most of northern Italy and the Low Countries and a secret clause promised the Republic of Venice to Austria. Bonaparte marched on Venice and forced its surrender, ending 1,100 years of independence; he also authorised the French to loot treasures such as the Horses of Saint Mark. His application of conventional military ideas to real-world situations effected his military triumphs, such as creative use of artillery as a mobile force to support his infantry. He referred to his tactics thus: "I have fought sixty battles and I have learned nothing which I did not know at the beginning. Look at Caesar; he fought the first like the last." He was adept at espionage and deception and could win battles by concealment of troop deployments and concentration of his forces on the 'hinge' of an enemy's weakened front. If he could not use his favourite envelopment strategy, he would take up the central position and attack two cooperating forces at their hinge, swing round to fight one until it fled, then turn to face the other. In this Italian campaign, Bonaparte's army captured 150,000 prisoners, 540 cannons and 170 standards. The French army fought 67 actions and won 18 pitched battles through superior artillery technology and Bonaparte's tactics.

During the campaign, Bonaparte became increasingly influential in French politics. He published two newspapers, ostensibly for the troops in his army, but widely circulated in France as well, and in May 1797, founded a third newspaper, Le Journal de Bonaparte et des hommes vertueux, which was published in Paris. Elections in mid-1797 gave the royalist party more power and alarmed the Directory. The royalists attacked Bonaparte for looting Italy and claimed he had overstepped his authority in dealings with the Austrians. Bonaparte sent General Pierre Augereau to Paris to lead a coup d'état and purge the royalists on 4 September — 18 Fructidor. This left Barras and his Republican allies in control again, but dependent on Bonaparte who proceeded to peace negotiations with Austria. These negotiations resulted in the Treaty of Campo Formio, and Bonaparte returned to Paris in December as a hero, more popular than the Directors. He met with Talleyrand, France's new Foreign Minister — who would later serve in the same capacity for Emperor Napoleon — and they began to prepare for an invasion of England. After two months of planning, Bonaparte decided France's naval power was not yet strong enough to confront the Royal Navy in the English Channel and proposed a military expedition to seize Egypt and thereby undermine Britain's access to its trade interests in India. Bonaparte wished to establish a French presence in the Middle East, with the ultimate dream of linking with a Muslim enemy of the British in India, Tipu Sultan. Napoleon assured the Directory that "as soon as he had conquered Egypt, he will establish relations with the Indian princes and, together with them, attack the English in their possessions." According to a February 1798 report by Talleyrand: "Having occupied and fortified Egypt, we shall send a force of 15,000 men from Suez to India, to join the forces of Tipu-Sahib and drive away the English." The Directory, though troubled by the scope and cost of the enterprise, agreed so the popular general would be absent from the centre of power.

In May 1798, Bonaparte was elected a member of the French Academy of Sciences. His Egyptian expedition included a group of 167 scientists: mathematicians, naturalists, chemists and geodesists among them; their discoveries included the Rosetta Stone and their work was published in the Description de l'Égypte in 1809. En route to Egypt, Bonaparte reached Malta on 9 June 1798, then controlled by the Knights Hospitaller. The two hundred Knights of French origin did not support the Grand Master, Prussian Ferdinand von Hompesch zu Bolheim, who had succeeded a Frenchman, and made it clear they would not fight against their compatriots. Hompesch surrendered after token resistance and Bonaparte captured a very important naval base with the loss of only three men. General Bonaparte and his expedition eluded pursuit by the Royal Navy and on 1 July landed at Alexandria. Bonaparte successfully fought the Battle of Chobrakit against the Mamluks, an old power in the Middle East. This helped the French plan their attack in the Battle of the Pyramids fought over a week later, about 6 km from the pyramids. General Bonaparte's forces were greatly outnumbered by the Mamluks' cavalry — 20,000 against 60,000 — but he formed hollow squares with supplies kept safely inside. 300 French and approximately 6,000 Egyptians were killed. On 1 August, the British fleet under Horatio Nelson captured or destroyed all but two French vessels in the Battle of the Nile and Bonaparte's goal of a strengthened French position in the Mediterranean Sea was frustrated. His army had nonetheless succeeded in a temporary increase of French power in Egypt, though it faced repeated uprisings. In early 1799, he moved the army into the Ottoman province of Damascus (Syria and Galilee). Bonaparte led these 13,000 French soldiers in the conquest of the coastal towns of Arish, Gaza, Jaffa, and Haifa. The attack on Jaffa was particularly brutal: Bonaparte, on discovering many of the defenders were former prisoners of war, ostensibly on parole, ordered the garrison and 1,400 prisoners to be executed by bayonet or drowning to save bullets. Men, women and children were robbed and murdered for three days.

With his army weakened by disease — mostly bubonic plague — and poor supplies, Bonaparte was unable to reduce the fortress of Acre, and returned to Egypt in May. To speed up the retreat, he ordered plague-stricken men to be poisoned. His supporters have argued this decision was necessary given the continued harassment of stragglers by Ottoman forces, and indeed those left behind alive were tortured and beheaded by the Ottomans. Back in Egypt, on 25 July, Bonaparte defeated an Ottoman amphibious invasion at Abukir. While in Egypt, Bonaparte stayed informed of European affairs through irregular delivery of newspapers and dispatches. He learned France had suffered a series of defeats in the War of the Second Coalition. On 24 August 1799, he took advantage of the temporary departure of British ships from French coastal ports and set sail for France, despite the fact he had received no explicit orders from Paris. The army was left in the charge of Jean Baptiste Kléber. Unknown to Bonaparte, the Directory had sent him orders to return to ward off possible invasions of French soil but poor lines of communication meant the messages had failed to reach him. By the time he reached Paris in October, France's situation had been improved by a series of victories. The Republic was bankrupt, however, and the ineffective Directory was unpopular with the French population. The Directory discussed Bonaparte's "desertion" but was too weak to punish him.

Bonaparte was approached by one of the Directors, Emmanuel Joseph Sieyès, for his support in a coup to overthrow the constitutional government. The leaders of the plot included his brother Lucien Bonaparte; the speaker of the Council of Five Hundred, Roger Ducos; another Director, Joseph Fouché; and Talleyrand. On 9 November — 18 Brumaire by the French Republican Calendar — Bonaparte was charged with the safety of the legislative councils, who were persuaded to remove to the Château de Saint-Cloud, to the west of Paris, after a rumour of a Jacobin rebellion was spread by the plotters. By the following day, the deputies had realised they faced an attempted coup. Faced with their remonstrations, Bonaparte led troops to seize control and disperse them, which left a rump legislature to name Bonaparte, Sièyes, and Ducos as provisional Consuls to administer the government. Though Sieyès expected to dominate the new regime, he was outmanoeuvred by Bonaparte, who drafted the Constitution of the Year VIII and secured his own election as First Consul. This made Bonaparte the most powerful person in France and he took up residence at the Tuileries.

In 1800, Bonaparte and his troops crossed the Alps into Italy, where French forces had been almost completely driven out by the Austrians whilst he was in Egypt. The campaign began badly for the French after Bonaparte made strategic errors; one force was left besieged at Genoa but managed to hold out and thereby occupy Austrian resources. This effort, and French general Desaix's timely reinforcements, allowed Bonaparte narrowly to avoid defeat and to triumph over the Austrians in June at the significant Battle of Marengo. Bonaparte's brother Joseph led the peace negotiations in Lunéville and reported that Austria, emboldened by British support, would not recognise France's newly gained territory. As negotiations became increasingly fractious, Bonaparte gave orders to his general Moreau to strike Austria once more. Moreau led France to victory at Hohenlinden. As a result, the Treaty of Lunéville was signed in February 1801; the French gains of the Treaty of Campo Formio were reaffirmed and increased.

Bonaparte set up a camp at Boulogne-sur-Mer to prepare for an invasion of Britain but both countries had become tired of war and signed the Treaty of Amiens in October 1801 and March 1802; this included the withdrawal of British troops from most colonial territories it had recently occupied. The peace was uneasy and short-lived; Britain did not evacuate Malta as promised and protested against Bonaparte's annexation of Piedmont and his Act of Mediation, which established a new Swiss Confederation, though neither of these territories were covered by the Treaty. The dispute culminated in a declaration of war by Britain in May 1803, and he reassembled the invasion camp at Boulogne.

Bonaparte faced a major setback and eventual defeat in the Haitian Revolution. By the Law of 20 May 1802 Bonaparte re-established slavery in France's colonial possessions, where it had been banned following the Revolution. Following a slave revolt, he sent an army to reconquer Saint-Domingue and establish a base. The force was, however, destroyed by yellow fever and fierce resistance led by Haitian generals Toussaint Louverture and Jean-Jacques Dessalines. Faced by imminent war against Britain and bankruptcy, he recognised French possessions on the mainland of North America would be indefensible and sold them to the United States — the Louisiana Purchase — for less than three cents per acre ($7.40 per km²).

Bonaparte instituted lasting reforms, including centralised administration of the departments, higher education, a tax code, road and sewer systems and the Banque de France — the country's central bank. He negotiated the Concordat of 1801 with the Catholic Church, which sought to reconcile the mostly Catholic population to his regime. It was presented alongside the Organic Articles, which regulated public worship in France. Later that year, Bonaparte became President of the French Academy of Sciences and appointed Jean Baptiste Joseph Delambre its Permanent Secretary. In May 1802, he instituted the Légion d'Honneur, a substitute for the old royalist decorations and orders of chivalry, to encourage civilian and military achievements; the order is still the highest decoration in France. His powers were increased by the Constitution of the Year X including: Article 1. The French people name, and the Senate proclaims Napoleon-Bonaparte First Consul for Life. After this he was generally referred to as Napoleon rather than Bonaparte. Napoleon's set of civil laws, the Code Civil — now often known as the Napoleonic code — was prepared by committees of legal experts under the supervision of Jean Jacques Régis de Cambacérès, the Second Consul. Napoleon participated actively in the sessions of the Council of State that revised the drafts. The development of the Code was a fundamental change in the nature of the civil law legal system with its stress on clearly written and accessible law. Other codes were commissioned by Napoleon to codify criminal and commerce law; a Code of Criminal Instruction was published, which enacted rules of due process.

Napoleon faced royalist and Jacobin plots as France's ruler, including the Conspiration des poignards (Daggers conspiracy) in October 1800 and the Plot of the Rue Saint-Nicaise two months later. In January 1804, his police uncovered an assassination plot against him which involved Moreau and which was ostensibly sponsored by the Bourbon former rulers of France. On the advice of Talleyrand, Napoleon ordered the kidnapping of the Duke of Enghien, in violation of neighbouring Baden's sovereignty. After a secret trial the Duke was executed, even though he had not been involved in the plot. Napoleon used the plot to justify the re-creation of a hereditary monarchy in France, with himself as Emperor, as a Bourbon restoration would be more difficult if the Bonapartist succession was entrenched in the constitution. Napoleon crowned himself Emperor Napoleon I on 2 December 1804 at Notre Dame de Paris and then crowned Joséphine Empress. At Milan Cathedral on 26 May 1805, Napoleon was crowned King of Italy with the Iron Crown of Lombardy. He created eighteen Marshals of the Empire from amongst his top generals, to secure the allegiance of the army. Ludwig van Beethoven, a long-time admirer, was disappointed at this turn towards imperialism, and scratched his dedication to Napoleon from his 3rd Symphony.

By 1805, Britain had convinced Austria and Russia to join a Third Coalition against France. Napoleon knew the French fleet could not defeat the Royal Navy in a head-to-head battle and planned to lure it away from the English Channel. The French Navy would escape from the British blockades of Toulon and Brest and threaten to attack the West Indies, thus drawing off the British defence of the Western Approaches, in the hope a Franco-Spanish fleet could take control of the Channel long enough for French armies to cross from Boulogne and invade England. However, after defeat at the naval Battle of Cape Finisterre in July 1805 and Admiral Villeneuve's retreat to Cadiz, invasion was never again a realistic option for Napoleon. Instead, he ordered the army stationed at Boulogne, his Grande Armée, to march to Germany secretly in a turning movement — the Ulm Campaign. This encircled the Austrian forces about to attack France and severed their lines of communication. On 20 October 1805, the French captured 30,000 prisoners at Ulm, though the next day Britain's victory at the Battle of Trafalgar meant the Royal Navy gained control of the seas. Six weeks later, on the first anniversary of his coronation, Napoleon defeated Austria and Russia at Austerlitz. This ended the Third Coalition and he commissioned the Arc de Triomphe to commemorate the victory. Austria had to concede territory; the Peace of Pressburg led to the dissolution of the Holy Roman Empire and creation of the Confederation of the Rhine with Napoleon named as its Protector. Napoleon would go on to say, "The battle of Austerlitz is the finest of all I have fought." Frank McLynn suggests Napoleon was so successful at Austerlitz he lost touch with reality, and what used to be French foreign policy became a "personal Napoleonic one". Vincent Cronin disagrees, stating Napoleon was not overly ambitious for himself, that "he embodied the ambitions of thirty million Frenchmen".

Even after the failed campaign in Egypt, Napoleon continued to entertain a grand scheme to establish a French presence in the Middle East. An alliance with Middle-Eastern powers would have the strategic advantage of pressuring Russia on its southern border. From 1803, Napoleon went to considerable lengths to try to convince the Ottoman Empire to fight against Russia in the Balkans and join his anti-Russian coalition. Napoleon sent General Horace Sebastiani as envoy extraordinary, promising to help the Ottoman Empire recover lost territories. In February 1806, following Napoleon's victory at Austerlitz and the ensuing dismemberment of the Habsburg Empire, the Ottoman Emperor Selim III finally recognized Napoleon as Emperor, formally opting for an alliance with France "our sincere and natural ally", and war with Russia and England. A Franco-Persian alliance was also formed, from 1807 to 1809, between Napoleon and the Persian Empire of Fath Ali Shah, against Russia and Great Britain. The alliance ended when France allied with Russia and turned its focus to European campaigns.

The Fourth Coalition was assembled in 1806, and Napoleon defeated Prussia at the Battle of Jena-Auerstedt in October. He marched against advancing Russian armies through Poland, and was involved in the bloody stalemate of the Battle of Eylau on 6 February 1807. After a decisive victory at Friedland, he signed the Treaties of Tilsit; one with Tsar Alexander I of Russia which divided the continent between the two powers; the other with Prussia which stripped that country of half its territory. Napoleon placed puppet rulers on the thrones of German states, including his brother Jérôme as king of the new Kingdom of Westphalia. In the French-controlled part of Poland, he established the Duchy of Warsaw with King Frederick Augustus I of Saxony as ruler. With his Milan and Berlin Decrees, Napoleon attempted to enforce a Europe-wide commercial boycott of Britain called the Continental System. This act of economic warfare did not succeed, as it encouraged British merchants to smuggle into continental Europe and Napoleon's exclusively land-based customs enforcers could not stop them. Portugal did not comply with the Continental System so, in 1807, Napoleon invaded with the support of Spain. Under the pretext of a reinforcement of the Franco-Spanish army occupying Portugal, Napoleon invaded Spain as well, replaced Charles IV with his brother Joseph and placed his brother-in-law Joachim Murat in Joseph's stead at Naples. This led to resistance from the Spanish army and civilians in the Dos de Mayo Uprising. Following a French retreat from much of the country, Napoleon took command and defeated the Spanish Army. He retook Madrid, then outmanoeuvred a British army sent to support the Spanish and drove it to the coast. Before the Spanish population had been fully subdued, Austria again threatened war and Napoleon returned to France. The costly and often brutal Peninsular War continued in Napoleon's absence; in the second Siege of Saragossa most of the city was destroyed and over 50,000 people perished. Although Napoleon left 300,000 of his finest troops to battle Spanish guerrillas as well as British and Portuguese forces commanded by Arthur Wellesley, 1st Duke of Wellington, French control over the peninsula again deteriorated. Following several allied victories, the war concluded after Napoleon's abdication in 1814. Napoleon later described the Peninsular War as central to his final defeat, writing in his memoirs That unfortunate war destroyed me... All... my disasters are bound up in that fatal knot.

In April 1809, Austria abruptly broke its alliance with France and Napoleon was forced to assume command of forces on the Danube and German fronts. After early successes, the French faced difficulties in crossing the Danube and suffered a defeat in May at the Battle of Aspern-Essling near Vienna. The Austrians failed to capitalise on the situation and allowed Napoleon's forces to regroup. He defeated the Austrians again at Wagram and a new peace, the Treaty of Schönbrunn, was signed between Austria and France. Britain was the other member of the coalition. In addition to the Iberian Peninsula, the British planned to open another front in mainland Europe. However, Napoleon was able to rush reinforcements to Antwerp, owing to Britain's inadequately organised Walcheren Campaign. He concurrently annexed the Papal States because of the Church's refusal to support the Continental System; Pope Pius VII responded by excommunicating the emperor. The Pope was then abducted by Napoleon's officers, and though Napoleon had not ordered his abduction, he did not order Pius' release. The Pope was moved throughout Napoleon's territories, sometimes while ill, and Napoleon sent delegations to pressure him on issues including agreement to a new concordat with France, which Pius refused. In 1810 Napoleon married the Austrian Marie Louise, Duchess of Parma, following his divorce of Joséphine; this further strained his relations with the Church and thirteen cardinals were imprisoned for non-attendance at the marriage ceremony. The Pope remained confined for 5 years, and did not return to Rome until May 1814. Napoleon consented to the ascent to the Swedish throne of Bernadotte, one of his marshals and a long-term rival of Napoleon's, in November 1810. Napoleon had indulged Bernadotte's indiscretions because he was married to Désirée Clary, but came to regret sparing his life when Bernadotte later allied Sweden with France's enemies.

The Congress of Erfurt sought to preserve the Russo-French alliance and the leaders had a friendly personal relationship after their first meeting at Tilsit in 1807. By 1811, however, tensions between the two nations had increased and Alexander was under pressure from the Russian nobility to break off the alliance. The first clear sign the alliance had deteriorated was the relaxation of the Continental System in Russia, which angered Napoleon. By 1812, advisers to Alexander suggested the possibility of an invasion of the French Empire and the recapture of Poland. On receipt of intelligence reports on Russia's war preparations, Napoleon expanded his Grande Armée to more than 450,000 men. He ignored repeated advice against an invasion of the vast Russian heartland and prepared for an offensive campaign; on 23 June 1812, his invasion of Russia commenced. In an attempt to gain increased support from Polish nationalists and patriots, Napoleon termed the war the Second Polish War — the First Polish War had been the Bar Confederation uprising by Polish nobles against Russia in 1768. Polish patriots wanted the Russian part of Poland to be joined with the Duchy of Warsaw and an independent Poland created. This was rejected by Napoleon, who stated he had promised his ally Austria this would not happen. Napoleon refused to manumit the Russian serfs, because of concerns this might provoke a reaction in his army's rear. The serfs would later commit atrocities against French soldiers during France's retreat. The Russians avoided Napoleon's objective of a decisive engagement and instead retreated deeper into Russia. A brief attempt at resistance was made at Smolensk in August; the Russians were defeated in a series of battles and Napoleon resumed his advance. The Russians again avoided battle, although in a few cases this was only achieved because Napoleon uncharacteristically hesitated to attack when the opportunity arose. Owing to the Russian army's scorched earth tactics, the French found it increasingly difficult to forage food for themselves and their horses. The Russians eventually offered battle outside Moscow on 7 September: the Battle of Borodino resulted in approximately 44,000 Russian and 35,000 French, dead, wounded or captured, and may have been the bloodiest day of battle in history up to that point in time. Although the French had won, the Russian army had accepted, and withstood, the major battle Napoleon had hoped would be decisive. Napoleon's own account was: "The most terrible of all my battles was the one before Moscow. The French showed themselves to be worthy of victory, but the Russians showed themselves worthy of being invincible." The Russian army withdrew and retreated past Moscow. Napoleon entered the city, assuming its fall would end the war and Alexander would negotiate peace. However, on orders of the city's governor Fyodor Rostopchin, rather than capitulation, Moscow was ordered burned. After a month, concerned about loss of control back in France, Napoleon and his army left.

The French suffered greatly in the course of a ruinous retreat, including from the harshness of the Russian Winter. The Armée had begun as over 400,000 frontline troops, but in the end fewer than 40,000 crossed the Berezina River in November 1812, to escape. The Russians had lost 150,000 in battle and hundreds of thousands of civilians. There was a lull in fighting over the winter of 1812–13 while both the Russians and the French rebuilt their forces; Napoleon was then able to field 350,000 troops. Heartened by France's loss in Russia, Prussia joined with Austria, Sweden, Russia, Great Britain, Spain, and Portugal in a new coalition. Napoleon assumed command in Germany and inflicted a series of defeats on the Coalition culminating in the Battle of Dresden in August 1813. Despite these successes, the numbers continued to mount against Napoleon and the French army was pinned down by a force twice its size and lost at the Battle of Leipzig. This was by far the largest battle of the Napoleonic Wars and cost more than 90,000 casualties in total. Napoleon withdrew back into France, his army reduced to 70,000 soldiers and 40,000 stragglers, against more than three times as many Allied troops. The French were surrounded: British armies pressed from the south, and other Coalition forces positioned to attack from the German states. Napoleon won a series of victories in the Six Days Campaign, though these were not significant enough to turn the tide and Paris was captured by the Coalition in March 1814. When Napoleon proposed the army march on the capital, his marshals decided to mutiny. On 4 April, led by Ney, they confronted Napoleon. Napoleon asserted the army would follow him and Ney replied the army would follow its generals. Napoleon had no choice but to abdicate. He did so in favour of his son; however, the Allies refused to accept this and Napoleon was forced to abdicate unconditionally on 11 April. In the Treaty of Fontainebleau the victors exiled him to Elba, an island of 12,000 inhabitants in the Mediterranean, 20 km off the Tuscan coast. They gave him sovereignty over the island and allowed him to retain his title of Emperor. Napoleon attempted suicide with a pill he had carried since a near-capture by Russians on the retreat from Moscow. Its potency had weakened with age and he survived to be exiled, while his wife and son took refuge in Vienna. In the first few months on Elba he created a small navy and army, developed the iron mines, and issued decrees on modern agricultural methods.

Separated from his wife and son, who had come under Austrian control, cut off from the allowance guaranteed to him by the Treaty of Fontainebleau, and aware of rumours he was about to be banished to a remote island in the Atlantic Ocean, Napoleon escaped from Elba on 26 February 1815. He landed at Golfe-Juan on the French mainland, two days later. The 5th Regiment was sent to intercept him and made contact just south of Grenoble on 7 March 1815. Napoleon approached the regiment alone, dismounted his horse and, when he was within gunshot range, shouted, "Here I am. Kill your Emperor, if you wish." The soldiers responded with, "Vive L'Empereur!" and marched with Napoleon to Paris; Louis XVIII fled. On 13 March, the powers at the Congress of Vienna declared Napoleon an outlaw and four days later Great Britain, the Netherlands, Russia, Austria and Prussia bound themselves to put 150,000 men into the field to end his rule. Napoleon arrived in Paris on 20 March and governed for a period now called the Hundred Days. By the start of June the armed forces available to him had reached 200,000 and he decided to go on the offensive to attempt to drive a wedge between the oncoming British and Prussian armies. The French Army of the North crossed the frontier into the United Kingdom of the Netherlands, in modern-day Belgium. Napoleon's forces fought the allies, led by Wellington and Gebhard Leberecht von Blücher, at the Battle of Waterloo on 18 June 1815. Wellington's army withstood repeated attacks by the French and drove them from the field while the Prussians arrived in force and broke through Napoleon's right flank. The French army left the battlefield in disorder, which allowed Coalition forces to enter France and restore Louis XVIII to the French throne. Off the port of Rochefort, Charente-Maritime, after consideration of an escape to the United States, Napoleon formally demanded political asylum from the British Captain Frederick Maitland on HMS Bellerophon on 15 July 1815. Napoleon was imprisoned and then exiled to the island of Saint Helena in the Atlantic Ocean, 2,000 km from any major landmass. In his first two months there, he lived in a pavilion on the Briars estate, which belonged to a William Balcombe. Napoleon became friendly with his family, especially his younger daughter Lucia Elizabeth who later wrote Recollections of the Emperor Napoleon. This friendship ended in 1818 when British authorities became suspicious that Balcombe had acted as an intermediary between Napoleon and Paris, and dismissed him from the island. Napoleon moved to Longwood House in December 1815; it had fallen into disrepair, and the location was damp, windswept and unhealthy. The Times published articles insinuating the British government was trying to hasten his death and he often complained of the living conditions in letters to the governor and his custodian, Hudson Lowe. With a small cadre of followers, Napoleon dictated his memoirs and criticised his captors — particularly Lowe. Lowe's treatment of Napoleon is regarded as poor by historians such as Frank McLynn. Lowe exacerbated a difficult situation through measures including a reduction in Napoleon's expenditure, a rule that no gifts could be delivered to him if they mentioned his imperial status, and a document his supporters had to sign that guaranteed they would stay with the prisoner indefinitely.

In 1818, The Times reported a false rumour of Napoleon's escape and said the news had been greeted by spontaneous illuminations in London. There was sympathy for him in the British Parliament: Lord Holland gave a speech which demanded the prisoner be treated with no unnecessary harshness. Napoleon kept himself informed of the events through The Times and hoped for release in the event that Holland became Prime Minister. He also enjoyed the support of Lord Cochrane, who was involved in Chile's and Brazil's struggle for independence and wanted to rescue Napoleon and help him set up a new empire in South America, a scheme frustrated by Napoleon's death in 1821. There were other plots to rescue Napoleon from captivity including one from Texas, where exiled soldiers from the Grande Armée wanted a resurrection of the Napoleonic Empire in America. There was even a plan to rescue him with a primitive submarine. For Lord Byron, Napoleon was the epitome of the Romantic hero, the persecuted, lonely and flawed genius. The news that Napoleon had taken up gardening at Longwood also appealed to more domestic British sensibilities.

In February 1821, his health began to fail rapidly and, on 3 May, two British physicians who had recently arrived attended him and could only recommend palliatives. He died two days later, after confession, Extreme Unction and Viaticum at the hands of Father Ange Vignali. His last words were, "France, armée, tête d'armée, Joséphine." ("France, army, head of the army, Joséphine.") Napoleon's original death mask was created around 6 May, though it is not clear which doctor created it. In his will, he had asked to be buried on the banks of the Seine, but the British governor said he should be buried on St. Helena, in the Valley of the Willows. Hudson Lowe insisted the inscription should read 'Napoleon Bonaparte', Montholon and Bertrand wanted the Imperial title 'Napoleon' as royalty were signed by their first names only. As a result the tomb was left nameless. In 1840, Louis-Philippe, King of the French obtained permission from the British to return Napoleon's remains to France. The remains were transported aboard the frigate Belle-Poule, which had been painted black for the occasion and on 29 November she arrived in Cherbourg. The remains were transferred to the steamship Normandie, which transported them to Le Havre, up the Seine to Rouen and on to Paris. On 15 December, a state funeral was held. The hearse proceeded from the Arc de Triomphe down the Champs-Élysées, across the Place de la Concorde to the Esplanade des Invalides and then to the cupola in St Jérôme's Chapel, where it stayed until the tomb designed by Louis Visconti was completed. In 1861, Napoleon's remains were entombed in a porphyry sarcophagus in the crypt under the dome at Les Invalides.

Napoleon's physician, Francesco Antommarchi, led the autopsy which found the cause of death to be stomach cancer, though he did not sign the official report, stating, "What had I to do with... English reports?" Napoleon's father had died of stomach cancer though this was seemingly unknown at the time of the autopsy. Antommarchi found evidence of a stomach ulcer and it was the most convenient explanation for the British who wanted to avoid criticism over their care of the Emperor. In 1955, the diaries of Napoleon's valet, Louis Marchand, appeared in print. His description of Napoleon in the months before his death led Sten Forshufvud to put forward other causes for his death, including deliberate arsenic poisoning, in a 1961 paper in Nature. Arsenic was used as a poison during the era because it was undetectable when administered over a long period. Forshufvud, in a 1978 book with Ben Weider, noted the emperor's body was found to be remarkably well-preserved when moved in 1840. Arsenic is a strong preservative and therefore this supported the poisoning hypothesis. Forshufvud and Weider observed that Napoleon had attempted to quench abnormal thirst by drinking high levels of orgeat syrup that contained cyanide compounds in the almonds used for flavouring. They maintained that the potassium tartrate used in his treatment prevented his stomach from expellation of these compounds and that the thirst was a symptom of poisoning. Their hypothesis was that the calomel given to Napoleon became an overdose, which killed him and left behind extensive tissue damage. A 2007 article stated that the type of arsenic found in Napoleon's hair shafts was mineral type, the most toxic, and according to toxicologist Dr Patrick Kintz, this supported the conclusion that his death was murder. The wallpaper used in Longwood contained a high level of arsenic compound used for colouring by British manufacturers. The adhesive, which in the cooler British environment was innocuous, may have grown mold in the more humid climate and emitted the poisonous gas arsine. This theory has been ruled out as it does not explain the arsenic absorption patterns found in other analyses. A 2004 group of researchers claimed treatments imposed on the emperor accidentally caused death by Torsades de pointes — a condition in which the heart ceases to function properly.

There have been modern studies which have supported the original autopsy finding. Researchers, in a 2008 study, analysed samples of Napoleon's hair from throughout his life, and from his family and other contemporaries. All samples had high levels of arsenic, approximately 100 times higher than the current average. According to these researchers, Napoleon's body was already heavily contaminated with arsenic as a boy, and the high arsenic concentration in his hair was not due to intentional poisoning; people were constantly exposed to arsenic from glues and dyes, throughout their lives. A 2007 study found no evidence of arsenic poisoning in the relevant organs and stated that stomach cancer was the cause of death.