Lord Mountbatten was born as His Serene Highness Prince Louis of Battenberg, although his German styles and titles were dropped in 1917. He was the youngest child and the second son of Prince Louis of Battenberg and his wife Princess Victoria of Hesse and by Rhine. His maternal grandparents were Ludwig IV, Grand Duke of Hesse and by Rhine and Princess Alice of the United Kingdom, who was a daughter of Queen Victoria and Prince Albert of Saxe - Coburg and Gotha. His paternal grandparents were Prince Alexander of Hesse and Princess Julia of Battenberg. His paternal grandparents' marriage was morganatic, because his grandmother was not of royal lineage; as a result, he and his father were styled "Serene Highness" rather than "Royal Highness," were not eligible to be titled Princes of Hesse and were given the less desirable Battenberg title. His siblings were Princess Alice of Greece and Denmark (mother of Prince Philip, Duke of Edinburgh), Queen Louise of Sweden, and George Mountbatten, 2nd Marquess of Milford Haven.

His father's forty-five year career reached its pinnacle in 1912 when he was appointed as First Sea Lord in the Admiralty. However, two years later in 1914, due to the growing anti-German sentiments that swept across Europe during the first few months of World War I and a series of lost battles at sea, Prince Louis felt it was his duty to step down from the position. In 1917, when the Royal Family stopped using their German names and titles, Prince Louis of Battenberg became Louis Mountbatten, and was created Marquess of Milford Haven. His second son acquired the courtesy title Lord Louis Mountbatten and was known as Lord Louis informally until his death notwithstanding his being granted a viscountcy in recognition of his wartime service in the Far East and an earldom for his role in the transition of India from British dependency to sovereign state.

Mountbatten was home schooled for the first ten years of his life. He was then sent to Lockers Park School in Hertfordshire and finally he followed his older brother to the Naval Cadet School. In childhood he visited the Imperial Court of Russia at St Petersburg and became intimate with the doomed Russian Imperial Family; in later life he was called upon authoritatively to rebut claims by pretenders to be the supposedly surviving Grand Duchess Anastasia. As a young man he had romantic feelings towards Anastasia's sister, the Grand Duchess Maria, and until the end of his life he kept her photograph at his bedside. After his nephew's change of name and engagement to the future Queen, he is alleged to have referred to the United Kingdom's dynasty as the future "House of Mountbatten", whereupon the Dowager Queen Mary reportedly refused to have anything to do with "that Battenberg nonsense", and the name of the Royal house remains Windsor by subsequent Royal decree — this can, however, be changed on the Monarch's wishes. After the marriage of Elizabeth II and Prince Philip, it was decreed that their non-royal descendants were to bear the (maiden) surname "Mountbatten - Windsor". Less than a week after the King's funeral, the new Queen's Uncle Dickie announced to guests at Broadlands that "The House of Mountbatten now reigns!"

Lord Mountbatten served in the Royal Navy as a midshipman during World War I. After his service, he attended Christ's College, Cambridge, for two terms where he studied engineering in a program that was specially designed for ex-servicemen. During his time at Cambridge, Mountbatten had to balance his studies with the robust social life he enjoyed as a member of Christ's College. In 1922, Mountbatten accompanied Edward, Prince of Wales, on a royal tour of India. It was during this trip that he met and proposed to his wife-to-be Edwina Ashley. They wed on 18 July 1922. Edward and Mountbatten formed a close friendship during the trip but their bond deteriorated during the Abdication Crisis. Mountbatten's loyalties between the wider Royal Family and the throne, on the one hand, and the then-King, on the other, were tested. Mountbatten came down firmly on the side of Prince Albert, the Duke of York, who was to assume the throne as George VI in his brother's place.

Pursuing his interests in technological development and gadgetry, Mountbatten joined the Portsmouth Signal School in 1924 and then went on to briefly study electronics at Greenwich before returning to military service. Mountbatten was a Member of the Institution of Electrical Engineers (IEE), and the successor organisation, the Institution of Engineering and Technology (IET), annually awards the Mountbatten Medal for an outstanding contribution, or contributions over a period, to the promotion of electronics or information technology and their application.

In 1926, Mountbatten was appointed to Assistant Fleet Wireless and Signals Officer of the Mediterranean Fleet under the command of Admiral Sir Roger Keyes. Lord Mountbatten returned to the Signal School in 1929 as Senior Wireless Instructor. In 1931, he was again called back to military service when he was appointed Fleet Wireless Officer to the Mediterranean Fleet. It was during this time that he founded a Signal School in Malta and became acquainted with all the radio operators in the fleet.

In 1934, Mountbatten was appointed to his first command. His ship was a new destroyer which he was to sail to Singapore and exchange for an older ship. He successfully brought the older ship back to port in Malta. By 1936, Mountbatten had been appointed to the Admiralty at Whitehall as a member of the Fleet Air Arm.

In the late 1930s Mountbatten was issued his 2nd Patent (UK Number 508,956) for a system for maintaining a warship in a fixed position relative to another ship.

When war broke out in 1939, Mountbatten was moved to active service as commander of the 5th Destroyer Flotilla from aboard his ship the HMS Kelly, which was famous for its many daring exploits. In early May 1940, Mountbatten led a British convoy in through the fog to evacuate the Allied forces participating in the Namsos Campaign. It was also in 1940 that he invented the Mountbatten Pink naval camouflage pigment. His ship was sunk in May 1941 during the Battle of Crete.

In August 1941 Mountbatten was appointed captain of HMS Illustrious which lay in Norfolk, Virginia, for repairs following action at Malta in the Mediterranean in January. During this period of relative inactivity he paid a flying visit to Pearl Harbor, where he was not impressed with the poor state of readiness and a general lack of co-operation between the US Navy and US Army, including the absence of a joint HQ.

Mountbatten was a favourite of Winston Churchill (although after 1948 Churchill never spoke to him again since he was famously annoyed with Mountbatten's later role in the independence of India and Pakistan), and on 27 October 1941 Mountbatten replaced Roger Keyes as Chief of Combined Operations. His duties in this role consisted of planning commando raids across the English Channel and inventing new technical aids to assist with opposed landings. Mountbatten was in large part responsible for the planning and organization of The Raid at St. Nazaire in mid 1942: an operation resulting in the putting into disuse of one of the most heavily defended docks in Nazi occupied France until well after war's end, the ramifications of which greatly contributed to allied supremacy in the Battle of the Atlantic. He personally pushed through the disastrous Dieppe Raid of 19 August 1942 (which certain elements of the Allied military, notably Field Marshal Montgomery, felt was ill-conceived from the start). The raid on Dieppe was widely considered to be a disaster, with casualties (including those wounded and/or taken prisoner) numbering in the thousands, the great majority of them Canadians. Historian Brian Loring Villa concluded that Mountbatten conducted the raid without authority, but that his intention to do so was known to several of his superiors, who took no action to stop him. Three noteworthy technical achievements of Mountbatten and his staff include: (1) the construction of an underwater oil pipeline from the English coast to Normandy, (2) an artificial harbor constructed of concrete caissons and sunken ships, and (3) the development of amphibious Tank - Landing Ships. Another project that Mountbatten proposed to Churchill was Project Habakkuk. It was to be a massive and impregnable 600 meter aircraft carrier made from reinforced ice or "Pykrete." Habakkuk never was actualised due to its enormous price tag.

Mountbatten claimed that the lessons learned from the Dieppe Raid were necessary for planning the Normandy invasion on D-Day nearly two years later. However, military historians such as former Royal Marine Julian Thompson have written that these lessons should not have needed a debacle such as Dieppe to be recognised. Nevertheless, as a direct result of the failings of the Dieppe raid, The British made several innovations - most notably Hobart's Funnies - innovations which, in the course of the Normandy Landings, undoubtedly saved many lives on those three beach heads upon which commonwealth soldiers were landing (Gold Beach, Juno Beach, and Sword Beach).

As a result of the Dieppe raid, Mountbatten became a controversial figure in Canada, with the Royal Canadian Legion distancing itself from him during his visits there during his later career; his relations with Canadian veterans "remained frosty". Nevertheless, a Royal Canadian Sea Cadet corps (RCSCC #134 Admiral Mountbatten in Sudbury, Ontario) was named after him in 1946.

In October 1943, Churchill appointed Mountbatten the Supreme Allied Commander South East Asia Command. His less practical ideas were sidelined by an experienced planning staff led by Lt-Col. James Allason, though some, such as a proposal to launch an amphibious assault near Rangoon, got as far as Churchill before being quashed. He would hold the post until the South East Asia Command (SEAC) was disbanded in 1946.

During his time as Supreme Allied Commander of the Southeast Asia Theatre, his command oversaw the recapture of Burma from the Japanese by General William Slim. His diplomatic handling of General "Vinegar Joe" Stilwell -- his deputy and also the officer commanding the American China Burma India Theatre -- and Generalissimo Chiang Kai-shek, leader of the Chinese Nationalist forces, was as gifted as that of General Eisenhower with General Montgomery and Winston Churchill. A personal high point was the reception of the Japanese surrender in Singapore when British troops returned to the island to receive the formal surrender of Japanese forces in the region led by General Itagaki Seishiro on 12 September 1945, codenamed Operation Tiderace.

His experience in the region and in particular his perceived Labour sympathies at that time led to Clement Attlee appointing him Viceroy of India after the war, charged with overseeing the transition of British India to independence no later than 1948. Mountbatten's instructions emphasised a united India as a result of the transference of power but authorised him to adapt to a changing situation in order to get Britain out promptly with minimal reputational damage. These priorities in turn affected the way negotiations took place when independence was discussed, especially between divided parties of Hindus and Muslims.

Mountbatten was fond of Congress leader Nehru and his liberal outlook for the country. He felt differently about the Muslim leader Jinnah, but was aware of his power, stating "If it could be said that any single man held the future of India in the palm of his hand in 1947, that man was Mohammad Ali Jinnah. Whereas Jinnah argued for Muslim representation in a united India, Nehru and the British grew tired of negotiating and thought it would be better to give Muslims their own homeland rather than try to find a solution that Jinnah and the Indian National Congress would agree on.

Given the British government's urging to grant independence quickly, Mountbatten concluded that a united India was an unachievable goal and he resigned himself to accept a plan that called for the partitioning of an independent India and Pakistan. Mountbatten insisted on setting a set date for the transfer of power from the British to the Indians, arguing that a fixed timeline would convince Indians of his and the British government's sincerity in working towards a swift and efficient independence, excluding all possibilities of stalling the process. He also concluded that the situation was too unsettled to wait any longer than 1947. This was to have disastrous consequences for the people of the sub-continent. The hastening of the process of the handover of power would unleash an orgy of violence and retribution rarely seen before in the Indian sub-continent.

Among the Indian leaders, Gandhi emphatically insisted on maintaining a united India and for a while successfully rallied people to this goal. However, when Mountbatten's timeline put the prospect of actually attaining independence quickly, sentiments took a different turn. Given Mountbatten's determination, Nehru and Patel's inability to deal with the Muslim League and lastly Jinnah's obstinacy, all Indian party leaders (except Gandhi) were coming to accept the stance of Jinnah's plan of dividing India, which in turn eased Mountbatten's task. This ironically resulted in a position which was essentially a bargaining tool for Jinnah to gain greater concessions becoming an end in itself.

Mountbatten also developed a strong relationship with the Indian princes, who ruled those portions of India not directly under British rule. The historian Ramachandra Guha states in his book 'India After Gandhi' that Mountbatten intervention was decisive in persuading the vast majority of them to the advantages in opting for accession to the Indian Union. Thus the integration of the princely states can be viewed as one of the positive aspects of his legacy.

When India and Pakistan attained independence in the night from 14 to 15 August 1947, Mountbatten remained in New Delhi for ten months, serving as India's first governor general until June 1948, thus becoming independent India's first Head of State.

Notwithstanding his self-promotion of his own part in Indian independence — notably in the television series "The Life and Times of Admiral of the Fleet Lord Mountbatten of Burma", produced by his son-in-law Lord Brabourne, and Dominique Lapierre and Larry Collins's rather sensationalised Freedom at Midnight (as to which he was the main informant) — his record is seen as very mixed; one prominent view is that he hastened the independence process unduly and recklessly, foreseeing vast disruption and loss of life and not wanting this to occur on the British watch, but thereby actually causing it to occur, especially in Punjab and Bengal. These critics contend that Mountbatten cannot escape responsibility for the way in which events spiraled out of control in the run up to and after independence.

John Kenneth Galbraith, the Canadian - American Harvard University economist, who advised governments of India during the 1950s, became an intimate of Nehru and served as the American ambassador from 1961 – 63, was a particularly harsh critic of Mountbatten in this regard. The horrific casualties of the partition of the Punjab are luridly described in Collins' and LaPierre's Freedom at Midnight, as to which Mountbatten was the principal informant, and more latterly in Bapsi Sidhwa's novel Ice Candy Man (published in the United States as Cracking India), made into the film Earth.

After India, Mountbatten served from 1948 – 1950 as commander of a cruiser squadron in the Mediterranean Fleet. He then went on to serve as Fourth Sea Lord in the Admiralty from 1950 – 52 and then returned to the Mediterranean to serve as Commander - in - Chief, Mediterranean Fleet, for three years. Mountbatten served his final posting in the Admiralty as First Sea Lord from 1955 – 59, the position which his father had held some forty years prior. This was the first time in Royal Naval history that a father and son had gained so high a rank.

In his biography of Mountbatten, Philip Ziegler notes on his ambitious character:

"His vanity, though child like, was monstrous, his ambition unbridled. The truth, in his hands, was swiftly converted from what it was, to what it should have been. He sought to rewrite history with cavalier indifference to the facts to magnify his own achievements. There was a time when I became so enraged by what I began to feel was his determination to hoodwink me that I found it necessary to place on my desk a notice saying: REMEMBER, IN SPITE OF EVERYTHING, HE WAS A GREAT MAN."

While serving as First Sea Lord, his primary concerns dealt with devising plans on how the Royal Navy would keep shipping lanes open if Britain was hit with a nuclear attack. Today, this seems of minor importance but at the time few people comprehended the potential limitless destruction nuclear weapons possess and the ongoing dangers posed by the fallout. Military commanders did not understand the physics involved in a nuclear explosion. This becomes evident when Mountbatten had to be reassured that the fission reactions from the Bikini Atoll tests would not spread through the oceans and blow up the planet. As Mountbatten became more familiar with this new form of weaponry, he increasingly grew opposed to their use in combat yet at the same time he realised the potential nuclear energy had, especially with regards to submarines. Mountbatten clearly expresses his feelings towards the use of nuclear weapons in combat in his article "A Military Commander Surveys The Nuclear Arms Race," which was published shortly after his death in International Security in the winter of 1979 – 80. After leaving the Admiralty, Lord Mountbatten took the position of Chief of the Defence Staff. He served in this post for six years during which he was able to consolidate the three service departments of the military branch into a single Ministry of Defence.

Mountbatten was Governor of the Isle of Wight from 1969 until 1974 and then appointed the first Lord Lieutenant of the Isle of Wight in 1974. He kept the position until his death.

From 1967 until 1978, Mountbatten became president of the United World Colleges Organisation, then represented by a single college: that of Atlantic College in South Wales. Mountbatten supported the United World Colleges and encouraged heads of state, politicians and personalities throughout the world to share his interest. Under Mountbatten's presidency and personal involvement, the United World College of South East Asia was established in Singapore in 1971, followed by the United World College of the Pacific (now known as the Lester B Pearson United World College of the Pacific) in Victoria, Canada, in 1974. In 1978, Lord Mountbatten of Burma passed the Presidency to his great-nephew, HRH The Prince of Wales.

Peter Wright, in his book Spycatcher, claimed that in 1967 Mountbatten attended a private meeting with press baron and MI5 agent Cecil King, and the Government's chief scientific adviser, Solly Zuckerman. King and Peter Wright were members of a group of thirty MI5 officers who wanted to stage a coup against the then crisis stricken Labour Government of Harold Wilson, and King allegedly used the meeting to urge Mountbatten to become the leader of a Government of national salvation. Solly Zuckerman pointed out that it was treason, and the idea came to nothing because of Mountbatten's reluctance to act.

In 2006 the BBC documentary The Plot Against Harold Wilson alleged that there had been another plot involving Mountbatten to oust Wilson during his second term in office (1974 – 76). The period was characterised by high inflation, increasing unemployment and widespread industrial unrest. The alleged plot centred around right wing former military figures who were supposedly building private armies to counter the perceived threat from trade unions and the Soviet Union. They believed that the Labour Party, which is partly funded by affiliated trade unions, was unable and unwilling to counter these developments and that Wilson was either a Soviet agent or at the very least a Communist sympathiser, claims Wilson strongly denied. The documentary alleged that a coup plot was planned to overthrow Wilson and replace him with Mountbatten using the private armies and sympathisers in the military and MI5. The documentary stated that Mountbatten and other members of the British Royal Family supported the plot and were involved in its planning.

Wilson had long believed that there had been an MI5 sponsored plan to overthrow him. This suspicion was heightened in 1974 when the Army occupied Heathrow Airport on the grounds that it was training for a possible IRA attack there. Marcia Falkender, a senior aide and intimate friend of Wilson, asserted that the Prime Minister hadn't been informed of the exercise and that it was ordered as a practice run for a military takeover. Wilson was also convinced that a small group of right wing MI5 officers were conducting a smear campaign against him. Such allegations had previously been attributed to Wilson's paranoia, not least because in 1988, Peter Wright admitted that the allegations in his book were "unreliable" and greatly exaggerated. However the BBC documentary interviewed several new witnesses who gave new credibility to the allegations.

Crucially, the first official history of MI5, The Defence of the Realm published in 2009, tacitly confirmed that there was a plot against Wilson and that MI5 did have a file on him. Yet it also made clear that the plot was in no way official and that any activity centred around a small group of discontented officers. This much had already been confirmed by former cabinet secretary Lord Hunt, who concluded in a secret inquiry conducted in 1996 that, "There is absolutely no doubt at all that a few, a very few, malcontents in MI5 . . . a lot of them like Peter Wright who were rightwing, malicious and had serious personal grudges – gave vent to these and spread damaging malicious stories about that Labour government."

Mountbatten's role in the plotting remains unclear. At the very least he appears to have associated with people who were greatly concerned about the country in the 1970s and were prepared to consider acting against the Government. It also seems certain that he shared their concerns. However, even though the BBC documentary alleged that he had offered his services to the coup plotters, it cannot be confirmed that he actually would have led a coup had it come about. It is notable that any plots that were discussed never actually took place, perhaps because the number of people involved was so small that any chances of success were slim.

Mountbatten's nickname among family and friends was "Dickie," notable in that "Richard" was not among his given names. This was because his great-grandmother, Queen Victoria, suggested the nickname of "Nicky", however it got mixed up with the many Nickys of the Russian Imperial Family ("Nicky" was particularly used to refer to Nicholas II, the last Tsar) so they changed it to Dickie. Mountbatten was married on 18 July 1922 to Edwina Cynthia Annette Ashley, daughter of Wilfred William Ashley, later 1st Baron Mount Temple, himself a grandson of the 7th Earl of Shaftesbury. She was the favourite granddaughter of the Edwardian magnate Sir Ernest Cassel and the principal heir to his fortune. There followed a glamorous honeymoon tour of European courts and America which famously included a visit with Douglas Fairbanks, Mary Pickford, and Charlie Chaplin in Hollywood, Chaplin creating a widely seen home movie "Nice and Easy", featuring the talents of Fairbanks, Pickford, Chaplin, and the Mountbattens. They had two daughters: Patricia Mountbatten, 2nd Countess Mountbatten of Burma (born on 14 February 1924), and Lady Pamela Carmen Louise (Hicks) (born on 19 April 1929).

The couple, in some ways, seemed incompatible from the beginning. Lord Mountbatten's obsession with being organised led him to keep a very close watch on Edwina and he demanded her constant attention. Having no real hobby or passions and living the lifestyle of royalty, Edwina spent most of her time partying with the British and Indian elite, going on cruises and secluding herself at the couple's country house on weekends. Even with growing unhappiness on both their parts, Louis refused to get a divorce fearing that it would hinder his climb up the military command chain. There were charges of infidelity against both. Edwina's numerous affairs led Louis to pursue a relationship with a French woman named Yola Letellier. From this point forward their marriage disintegrated into constant accusations and suspicions. Throughout the 1930s both readily admitted to numerous affairs. World War II gave Edwina the opportunity to focus on something other than Louis' infidelity. She joined the St. John's Ambulance Brigade as an administrator. This role gave Edwina the legacy of being a heroine of the Partition Period because of her efforts to ease the pain and suffering of the people in the Punjab.

It has been well documented that Edwina and India's first PM Jawaharlal Nehru became intimate friends after Indian Independence. During the summers, she would frequent the PM's house so she could lounge about on his veranda during the hot Delhi days. Personal correspondence between the two reveals a satisfying yet frustrating relationship. Edwina states in one of her letters "Nothing that we did or felt would ever be allowed to come between you and your work or me and mine -- because that would spoil everything." Despite this, it is still debated whether or not their relationship became physical. Both Mountbatten daughters have candidly acknowledged that their mother had a fiery temperament and was not always supportive of her husband when jealousy of his high profile overbore a sense of their having common cause. Lady Mountbatten died on 21 February 1960 at the age of 58 while in North Borneo inspecting medical facilities. Her death is thought to have been caused by a heart condition.

Until his assassination in 1979, Mountbatten kept a photograph of his cousin Grand Duchess Maria Nikolaevna of Russia, beside his bed in memory of the crush he once had upon her.

Since Mountbatten had no sons, when he was created Viscount on 23 August 1946, then Earl and Baron on 28 October 1947, the Letters Patent were drafted such that the titles would pass to the female line and its male issue. This was at his firm insistence: his relationship with his elder daughter had always been particularly close and it was his special wish that she succeed to the title in her own right. There was longstanding precedent for such remainders for military commanders: past examples included the 1st Viscount Nelson and the 1st Earl Roberts.

Like many members of the royal family, Mountbatten was an aficionado of polo, and received U.S. patent 1,993,334 in 1931 for a polo stick.

Mountbatten was a strong influence in the upbringing of his great-nephew, The Prince of Wales, and later as a mentor — "Honorary Grandfather" and "Honorary Grandson", they fondly called each other according to the Jonathan Dimbleby biography of the Prince — though according to both the Ziegler biography of Mountbatten and the Dimbleby biography of the Prince the results may have been mixed. He from time to time strongly upbraided the Prince for showing tendencies towards the idle pleasure - seeking dilettantism of his predecessor as Prince of Wales, King Edward VIII, later known as the Duke of Windsor, whom Mountbatten had known well in their youth. Yet he also encouraged the Prince to enjoy the bachelor life while he could and then to marry a young and inexperienced girl so as to ensure a stable married life.

Mountbatten's qualification for offering advice to this particular heir to the throne was unique; it was he who had arranged the visit of King George VI and Queen Elizabeth to Dartmouth Royal Naval College on 22 July 1939, taking care to include the young Princesses Elizabeth and Margaret in the invitation, but assigning his nephew, Cadet Prince Philip of Greece, to keep them amused while their parents toured the facility. This was the first recorded meeting of Charles's future parents. But a few months later, Mountbatten's efforts nearly came to naught when he received a letter from his sister Alice in Athens informing him that Philip was visiting her and had agreed to permanently repatriate to Greece. Within days, Philip received a command from his cousin and sovereign, King George II of Greece, to resume his naval career in Britain which, though given without explanation, the young prince obeyed.

In 1974 Mountbatten began corresponding with Charles about a potential marriage to his granddaughter, Hon. Amanda Knatchbull. It was about this time he also recommended that the 25 year old prince get on with sowing some wild oats. Charles dutifully wrote to Amanda's mother (who was also his godmother), Lady Brabourne, about his interest. Her answer was supportive, but advised him that she thought her daughter still rather young to be courted.

Four years later Mountbatten secured an invitation for himself and Amanda to accompany Charles on his planned 1980 tour of India. Their fathers promptly objected. Prince Philip thought that the Indian public's reception would more likely reflect response to the uncle than to the nephew. Lord Brabourne counselled that the intense scrutiny of the press would be more likely to drive Mountbatten's godson and granddaughter apart than together.

Charles was re-scheduled to tour India alone, but Mountbatten did not live to the planned date of departure. When Charles finally did propose marriage to Amanda, later in 1979, the circumstances were tragically changed, and she refused him.

On 27 April 1977, shortly before his 77th birthday, Mountbatten became the first member of the Royal Family to appear on the TV guest show This Is Your Life.

Mountbatten usually holidayed at his summer home in Mullaghmore, County Sligo, a small seaside village between Bundoran, County Donegal and Sligo, County Sligo, on the northwest coast of Ireland. Bundoran was a popular holiday destination for IRA volunteers, many of whom may have been aware of Mountbatten's presence and movements in Mullaghmore. Despite security advice and warnings from the Garda Síochána, on 27 August 1979, Mountbatten went lobster potting and tuna fishing in a thirty-foot (10 m) wooden boat, the Shadow V, which had been moored in the harbour at Mullaghmore. An IRA member named Thomas McMahon had slipped on to the unguarded boat that night and attached a radio controlled fifty pound (23 kg) bomb. When Mountbatten was on the boat en route to Donegal Bay, an unknown person detonated the bomb from shore. McMahon had been arrested earlier at a Garda checkpoint between Longford and Granard. Mountbatten, then aged 79, was seriously wounded and died soon after the blast by drowning while unconscious in the bay. Others killed in the blast were Nicholas Knatchbull, his elder daughter's 14 year old son; Paul Maxwell, a 15 year old youth from County Fermanagh who was working as a crew member; and Baroness Brabourne, his elder daughter's 83 year old mother-in-law who was seriously injured in the explosion, and died from her injuries the following day. Nicholas Knatchbull's mother and father, along with his twin brother Timothy, survived the explosion but were seriously injured.

Sinn Féin vice-president Gerry Adams said of Mountbatten's death:

The IRA gave clear reasons for the execution. I think it is unfortunate that anyone has to be killed, but the furore created by Mountbatten's death showed up the hypocritical attitude of the media establishment. As a member of the House of Lords, Mountbatten was an emotional figure in both British and Irish politics. What the IRA did to him is what Mountbatten had been doing all his life to other people; and with his war record I don't think he could have objected to dying in what was clearly a war situation. He knew the danger involved in coming to this country. In my opinion, the IRA achieved its objective: people started paying attention to what was happening in Ireland.

On the same day Mountbatten was assassinated, the IRA also ambushed and killed eighteen British Army soldiers, sixteen of them from the Parachute Regiment at Warrenpoint, County Down, in what became known as the Warrenpoint ambush.

Prince Charles took Mountbatten's death particularly hard, remarking to friends that things were never the same after losing his mentor. It has since been revealed that Mountbatten had been favourable towards the eventual reunification of Ireland.

The President of Ireland, Patrick Hillery, and the Taoiseach, Jack Lynch, attended a memorial service for Mountbatten in St. Patrick's Cathedral in Dublin. Mountbatten was buried in Romsey Abbey after a televised funeral in Westminster Abbey which he himself had comprehensively planned.

On 23 November 1979, Thomas McMahon was convicted of murder for his part in the bombing. He was released in 1998 under the terms of the Good Friday Agreement.

On hearing of Mountbatten's death, the then Master of the Queen's Music, Malcolm Williamson, was moved to write the Lament in Memory of Lord Mountbatten of Burma for violin and string orchestra. One of the most poignant of tributes paid to Mountbatten, the 11-minute work was given its first performance on 5 May 1980 by the Scottish Baroque Ensemble, conducted by Leonard Friedman.