Born in Nuremberg, Sigismund was the son of the Holy Roman Emperor Charles IV and of his fourth wife Elizabeth of Pomerania, the granddaughter of King Casimir III of Poland. King Louis the Great of Hungary and Poland always had a good and close relationship with Emperor Charles IV. Young Sigismund was sent to the Hungarian court, and soon learned the Hungarian language and Hungarian way of life, and became entirely devoted to his adopted country. King Louis appointed Sigismund to succeed him as King of Hungary; Louis named him his heir, and arranged the marriage with his eldest daughter Mary of Hungary. Accordingly, Sigismund was betrothed to Mary in 1374, who intended Mary to succeed him in the Kingdom of Poland with her future husband as was the custom of the time. Sigismund became Margrave of Brandenburg on his father's death in 1378.

In 1381, the then 13 year old Sigismund was sent to Kraków by his eldest brother and guardian Wenceslaus, King of the Romans, to learn Polish and to become acquainted with the land and its people. King Wenceslaus also gave him Neumark to facilitate communication between Brandenburg and Poland.

Because of his intrigues, Prince Sigismund was expelled from Poland, which was then given to Mary's younger sister Jadwiga I of Poland, who married Jogaila of Lithuania. When an opposing candidate for the Árpád throne appeared, Sigismund fled, leaving his wife Mary and her mother, Elizabeth of Bosnia at the mercy of conspirators. Years of civil war followed.

On the death of her father in 1382, his betrothed, Mary, became the Queen of Hungary and Sigismund married her in 1385 in Zólyom (today Zvolen). However she was captured, together with her mother who had acted as the Regent of Hungary, in the following year by the rebellious Horvathys, Bishop Paul of Machva, his brother Ivanish and younger brother Ladislaus. This followed an elaborate plan by the 17 year old Sigismund himself, and his mother - in - law was strangled (allegedly by Sigismund's men) in January 1387. Mary was only rescued in June 1387 through the aid of the Venetians (her first cousin once removed, King Stjepan Tvrtko I of Bosnia, then became an honorary Venetian citizen) and she was apparently reconciled with the Horvathys. Mary never forgave Sigismund for the death of her beloved mother, despite his claim to have punished the murderers, and they subsequently lived separate lives and had separate households. She died in 1395 in a suspicious horse accident while heavily pregnant.

Having secured the support of the nobility, Sigismund was crowned King of Hungary at Székesfehérvár on 31 March 1387. Having raised money by pledging Brandenburg to his cousin Jobst, margrave of Moravia (1388), he was engaged for the next nine years in a ceaseless struggle for the possession of this unstable throne. It was not for entirely selfless reasons that one of the leagues of barons helped him to power: Sigismund had to pay for the support of the lords by transferring a sizable part of the royal properties. (For some years, the baron's council governed the country in the name of the Holy Crown). The restoration of the authority of the central administration took decades of work. The bulk of the nation headed by the great Garai family was with him; but in the southern provinces between the Sava and the Drava, the Horvathys with the support of King Tvrtko I of Bosnia, Mary's maternal uncle, proclaimed as their king Ladislaus, king of Naples, son of the murdered Charles II of Hungary. Not until 1395 did Nicholas II Garay succeed in suppressing them. On a number of occasions, Sigismund was imprisoned by nobles, but guilefully bribed his way out.

In 1396 Sigismund led the combined armies of Christendom against the Turks, who had taken advantage of the temporary helplessness of Hungary to extend their dominion to the banks of the Danube. This crusade, preached by Pope Boniface IX, was very popular in Hungary. The nobles flocked in thousands to the royal standard, and were reinforced by volunteers from nearly every part of Europe, the most important contingent being that of the French led by John the Fearless, son of Philip II, Duke of Burgundy. Sigismund set out with 90,000 men and a flotilla of 70 galleys. After capturing Vidin, he camped with his Hungarian armies before the fortress of Nicopolis. Sultan Bayezid I raised the siege of Constantinople and, at the head of 140,000 men, completely defeated the Christian forces in the Battle of Nicopolis fought between 25 and 28 September 1396. He returned across the sea and through the realm of Zeta, where he ordained a local Serb lord Đurađ II with the islands of Hvar and Korčula for resistance against the Turks, which were returned to Sigismund after his death in April 1403.

The disaster in Nicopolis angered several Hungarian lords, which led to instability in the kingdom. Deprived of his authority in Hungary, Sigismund then turned his attention to securing the succession in Germany and Bohemia, and was recognized by his childless half brother Wenceslaus IV as Vicar - General of the whole Empire. However, he was unable to support Wenceslaus when he was deposed in 1400 and Rupert of Germany, Elector Palatine, was elected German king in his stead.

On his return to Hungary in 1401, Sigismund was once imprisoned and twice deposed. In 1401 Sigismund assisted a rising against Wenceslaus, during the course of which the Bohemian king was made a prisoner, and Sigismund ruled Bohemia for nineteen months. He released Wenceslaus in 1403. In the meantime, a group of Hungarian noblemen swore loyalty the last Anjou monarch, Ladislaus of Naples, putting their hands over the relic of Sain Ladislas of Hungary in Nagyvárad. Ladislaus was the son of the murdered Charles II of Hungary, and thus far relative from the long ago deceased king Louis I of Hungary. Ladislaus captured Zadar in 1403, but soon stopped military advances. This struggle in its turn led to a war with the Republic of Venice, as Ladislaus had sold the Dalmatian cities to the Venetians for 100,000 ducats before departing to his own land. In the following years Sigmismund acted indirectly to thwart Ladislaus' attempts to conquest central Italy, by allying with the Italian cities resisting him and by putting diplomatic pressure against him.

In 1404 he introduced the Placetum Regium. According to this decree, Papal bulls could not be pronounced in Hungary without the consent of the king.

In about 1406 he married Mary's cousin Barbara of Celje (Barbara Celjska, nicknamed the "Messalina of Germany"), daughter of Count Hermann II of Celje. Hermann's mother Katarina Kotromanić (of the House of Kotromanic) and Mary's mother Queen Elizabeta (Elisabeth of Bosnia) were sisters, or cousins who were adopted sisters. Tvrtko I was their first cousin and adopted brother, and perhaps even became heir apparent to Queen Mary. Tvrtko may have been murdered in 1391 on Sigismund's order.

He founded his personal order of knighthood, the Order of the Dragon, after this victory. Members of the order were mostly his political allies and supporters. The most important European monarchs became members of the order. He encouraged international trade by abolishing internal duties, regulating tariffs on foreign goods and standardizing weights and measures throughout the country. Due to his frequent absences attending to business in the other countries over which he ruled, he was obliged to consult Diets in Hungary with more frequency than his predecessors and institute the office of Palatine as chief administrator while he was away. During his long reign royal castle of Buda became probably the largest Gothic palace of the late Middle Ages.

In Slavonia he managed to establish control. He did not hesitate to use violent methods but from the river Sava to the south his control was weak. Sigismund personally led an army of almost 50,000 "crusaders" against the Croats and Bosnians, which culminated in 1408 with the Battle of Dobor, and a massacre of about 200 noble families, many of them victors of numerous battles against the Ottomans.

After the death of King Rupert of Germany in 1410, Sigismund – ignoring the claims of his half brother Wenceslaus – was elected as successor by three of the electors on 10 September 1410, but he was opposed by his cousin Jobst of Moravia, who had been elected by four electors in a different election on 1 October. Jobst's death 18 January 1411 removed this conflict and Sigismund was again elected King on 21 July 1411. His coronation was deferred until 8 November 1414, when it took place at Aachen.

On a number of occasions, and in 1410 in particular, Sigismund allied himself with the Teutonic Knights against Wladyslaw Jagiello of Poland. In return for 300.000 ducats he would attack Poland from the south after the truce on St. John's Day, 24 June expired. However, he was opposed by most of his noblemen and was prevented from participating in the alliance of twenty - two western states against Poland in the decisive Battle of Grünwald in July of that year.

In 1412 – 23 he campaigned against the Venetians in Italy. The king took advantage of the difficulties of Antipope John XXIII to obtain a promise that a council should be called at Constance in 1414 to settle the Western Schism. He took a leading part in the deliberations of this assembly, and during the sittings made a journey into France, England and Burgundy in a vain attempt to secure the abdication of the three rival popes. The council ended in 1418, solving the Schism and — of great consequence to Sigismund's future career — having the Czech religious reformer, Jan Hus, burned at the stake for heresy in July 1415. The complicity of Sigismund in the death of Hus is a matter of controversy. He had granted him a safe conduct and protested against his imprisonment; and the reformer was burned during his absence.

It was also at this Council that a cardinal ventured to correct Sigismund's Latin (he had construed the word schisma as feminine rather than neuter). To this Sigismund replied:

I am king of the Romans and above grammar.

An alliance with England against France, and an attempt to secure peace in Germany by a league of the towns, which failed owing to the hostility of the princes, were his main acts of these years. Also, Sigismund granted control of the Margraviate of Brandenburg (which he had received back after Jobst's death) to Frederick I of Hohenzollern, burgrave of Nuremberg (1415). This step made the Hohenzollern family one of the most important in Germany.

Sigismund, Holy Roman Emperor began to shift his alliance from France to England after the French defeat at the Battle of Agincourt. The Treaty of Canterbury (August 15, 1416) culminated diplomatic efforts between Henry V of England and Sigismund and resulted in a defensive and offensive alliance against France. This, in turn, led the way to resolution of the papal schism.

In 1419, the death of Wenceslaus IV left Sigismund titular King of Bohemia, but he had to wait for seventeen years before the Czechs would acknowledge him. Although the two dignities of King of the Romans and King of Bohemia added considerably to his importance, and indeed made him the nominal temporal head of Christendom, they conferred no increase of power and financially embarrassed him. It was only as King of Hungary that he had succeeded in establishing his authority and in doing anything for the order and good government of the land. Entrusting the government of Bohemia to Sofia of Bavaria, the widow of Wenceslaus, he hastened into Hungary.

The Bohemians, who distrusted him as the betrayer of Hus, were soon in arms; and the flame was fanned when Sigismund declared his intention of prosecuting the war against heretics. Three campaigns against the Hussites ended in disaster. The Turks were again attacking Hungary. The king, unable to obtain support from the German princes, was powerless in Bohemia. His attempts at the diet of Nuremberg in 1422 to raise a mercenary army were foiled by the resistance of the towns; and in 1424 the electors, among whom was Sigismund's former ally, Frederick I of Hohenzollern, sought to strengthen their own authority at the expense of the king. Although the scheme failed, the danger to Germany from the Hussites led to the Union of Bingen, which virtually deprived Sigismund of the leadership of the war and the headship of Germany.

In 1428 he led another campaign against the Turks, but again with few results. In 1431 he went to Milan where on 25 November he received the Iron Crown; after which he remained for some time at Sienna, negotiating for his coronation as emperor and for the recognition of the Council of Basel by Pope Eugenius IV. He was crowned emperor in Rome on 31 May 1433, and after obtaining his demands from the Pope returned to Bohemia, where he was recognized as king in 1436, though his power was little more than nominal.

He died in 9 December 1437 at Znojmo (German: Znaim), Moravia (now Czech Republic), and as ordered in life, he was buried at Nagyvárad, Hungary (today Oradea, Romania), next to the tomb of the king Saint Ladislaus I of Hungary, who was the ideal of the perfect monarch, warrior and Christian for that time and was deeply venerated by Sigismund. By his second wife, Barbara of Celje, he left an only daughter, Elisabeth of Bohemia (1409 – 1442), who was married to Albert V, duke of Austria (later German king as Albert II) whom Sigismund named as his successor. As he left no sons his line of the House of Luxembourg became extinct on his death.

Sigismund married twice but had little luck in securing the succession to his crowns. Each of his two marriages resulted in the birth of one child. His first born child, probably a son, was born prematurely as a result of a horse riding accident suffered by Queen Mary of Hungary when she was well advanced in pregnancy. Mother and child both died shortly after the birth in the hills of Buda on 17 May 1395. This caused a deep succession crisis because Sigismund ruled over Hungary by right of his wife, and although he managed to keep his power, the crisis lasted until his second marriage to Barbara of Celje. Barbara's only child, born in the purple on 7 October 1409, probably in the castle of Visegrád, was Elisabeth of Bohemia, the future queen consort of Hungary, Germany and Bohemia. Queen Barbara was unable to give birth to any further issue. Elisabeth of Bohemia was thus the only surviving legitimate offspring of Sigismund.