Ernest Shackleton was born on 15 February 1874 in Kilkea near Athy, County Kildare, Ireland, about 46 miles (74 km) from Dublin. Ernest's father was Henry Shackleton, and his mother was Henrietta Letitia Sophia Gavan. His father's family was Anglo-Irish, originally from Yorkshire, England. His mother's family was Irish, from counties Cork and Kerry. Ernest was the second of their ten children and the first of two sons; the second, Frank, achieved notoriety as a suspect, later exonerated, in the 1907 theft of the Irish Crown Jewels.

In 1880, when Ernest was six, Henry Shackleton gave up his life as a landowner to study Medicine at Trinity College, Dublin, moving his family into the city. Four years later, the family moved again, from Ireland to Sydenham in suburban London. Partly this was in search of better professional prospects for the newly qualified Doctor, but another factor may have been unease about their Anglo-Irish ancestry, following the assassination by Irish nationalists of Lord Frederick Cavendish, the British Secretary for Ireland, in 1882.

During the following four years at sea, Shackleton learned his trade, visiting the far corners of the earth and forming acquaintances with a variety of people from many walks of life, learning to be at home with all kinds of men. In August 1894, he passed his examination for Second Mate and accepted a post as third officer on a tramp steamer of the Welsh Shire Line. Two years later, he had obtained his First Mate's ticket, and in 1898, he was certified as a Master Mariner, qualifying him to command a British ship anywhere in the world.

Discovery departed London on 31 July 1901, arriving at the Antarctic coast, via Cape Town and New Zealand, on 8 January 1902. After landing, Shackleton took part in an experimental balloon FLIGHT on 4 February. He also participated, with the Scientists Edward Wilson and Hartley Ferrar, in the first sledging trip from the expedition's winter quarters in McMurdo Sound, a journey which established a safe route on to the Great Ice Barrier. During the Antarctic winter of 1902, in the confines of the iced-in Discovery, Shackleton edited the expedition's magazine The South Polar Times.

The party set out on 2 November 1902. The march was, Scott wrote later, "a combination of success and failure". A record Farthest South latitude of 82° 17' was reached, beating the previous record established in 1900 by Carsten Borchgrevink. The journey was marred by the poor performance of the dogs, whose food had become tainted, and who rapidly fell sick. All 22 dogs died during the march. The three men all suffered at times from snow blindness, frostbite and, ultimately, scurvy. On the return journey, Shackleton had by his own admission "broken down" and could no longer carry out his share of the work.

On 4 February 1903, the party finally reached the ship. After a medical examination (which proved inconclusive), Scott decided to send Shackleton home on the relief ship Morning, which had arrived in McMurdo Sound in January 1903. Scott wrote: "He ought not to risk further hardship in his present state of health." There is conjecture that Scott's motives for removing him was resentment of Shackleton's popularity, and that ill-health was used as an excuse to get rid of him.

After a period of convalescence in New Zealand, Shackleton returned to England via San Francisco and New York. As the first significant person to return from the Antarctic, he found that he was in demand; in particular, the Admiralty wished to consult him about its further proposals for the rescue of Discovery. With Sir Clements Markham's blessing, he accepted a temporary post assisting the outfitting of the Terra Nova for the second Discovery relief operation, but turned down the offer to sail with her as chief officer. He also assisted in the equipping of the Argentinean corvette Uruguay, which was being fitted out for the relief of the stranded Swedish Antarctic Expedition under Nordenskiöld. In search of more permanent employment, Shackleton applied for a regular commission in the Royal Navy, via the back-door route of the Supplementary List, but despite the sponsorship of Markham and of the President of the Royal Society, he was not successful. Instead, he became a Journalist, working for the Royal Magazine, but he found this unsatisfactory. He was then offered, and accepted, the secretaryship of the Royal Scottish Geographical Society (RSGS), a post which he took up on 11 January 1904. On 9 April 1904 he married Emily Dorman, with whom he had three children: Raymond, Cecily, and Edward.

In 1905, Shackleton became a shareholder in a speculative company that aimed to make a fortune transporting Russian troops home from the Far East. Despite his assurances to Emily that "we are practically sure of the contract", nothing came of this scheme. He also ventured into politics, unsuccessfully standing in the 1906 General Election as the Liberal Unionist Party's candidate for Dundee in opposition to Irish Home Rule. In the meantime he had taken a job with wealthy Clydeside industrialist william Beardmore (later Lord Invernairn), with a roving commission which involved interviewing prospective clients and entertaining Beardmore's Business friends. Shackleton by this time was making no secret of his ambition to return to Antarctica at the head of his own expedition.

Study of diaries kept by Eric Marshall, medical officer to the 1907–09 expedition, suggests that Shackleton suffered from an atrial septal defect ("hole in the heart"), a congenital heart defect, which may have been a cause of his health problems.

The "Great Southern Journey", as Frank Wild called it, began on 29 October 1908. On 9 January 1909, Shackleton and three companions (Wild, Eric Marshall and Jameson Adams) reached a new Farthest South latitude of 88° 23' S, a point only 112 miles (180 km) from the Pole. En route the South Pole party discovered the Beardmore Glacier (named after Shackleton's patron) and became the first persons to see and travel on the South Polar Plateau. Their return journey to McMurdo Sound was a race against starvation, on half-rations for much of the way. At one point, Shackleton gave his one biscuit allotted for the day to the ailing Frank Wild, who wrote in his diary: "All the money that was ever minted would not have bought that biscuit and the remembrance of that sacrifice will never leave me". They arrived at Hut Point just in time to catch the ship.

Several mostly intact cases of whisky and Brandy left behind in 1909 were recovered in 2010, for analysis by a distilling company. A revival of the vintage (and since lost) formula for the particular brands found has been offered for sale with a portion of the proceeds to benefit the New Zealand Antarctic Heritage Trust which discovered the lost spirits.

Any Future resumption by Shackleton of the quest for the South Pole depended on the results of Scott's Terra Nova Expedition, which left from Cardiff in July 1910. By early 1912, the world was aware that the pole had been conquered, by the Norwegian Roald Amundsen. The fate of Scott's expedition was not then known. Shackleton's mind turned to a project that had been announced, and then abandoned, by the Scottish Explorer william Speirs Bruce, for a continental crossing, from a landing in the Weddell Sea, via the South Pole to McMurdo Sound. Bruce, who had failed to acquire financial backing, was happy that Shackleton should adopt his plans, which were similar to those being followed by the German Explorer Wilhelm Filchner. Filchner had left Bremerhaven in May 1911; in December 1912, the news arrived from South Georgia that his expedition had failed. The transcontinental journey, in Shackleton's words, was the "one great object of Antarctic journeyings" remaining, now open to him.

After the race to the South Pole ended in December 1911 with Roald Amundsen's conquest, Shackleton turned his attention to the crossing of Antarctica from sea to sea, via the pole. To this end he made preparations for what became the Imperial Trans-Antarctic Expedition, 1914–17. Disaster struck this expedition when its ship, Endurance, became trapped in pack ice and was slowly crushed before the shore parties could be landed. The crew escaped by camping on the sea ice until it disintegrated, then by launching the lifeboats to reach Elephant Island and ultimately the inhabited island of South Georgia, a stormy ocean voyage of 720 nautical miles and Shackleton's most famous exploit. In 1921, he returned to the Antarctic with the Shackleton–Rowett Expedition, but died of a heart attack while his ship was moored in South Georgia. At his wife's request he was buried there.

Despite the outbreak of the First World War on 3 August 1914, Endurance was directed by the First Lord of the Admiralty, Winston Churchill, to "proceed", and left British waters on 8 August. Shackleton delayed his own departure until 27 September, meeting the ship in Buenos Aires.

Until this point, Shackleton had hoped that the ship, when released from the ice, could work her way back towards Vahsel Bay. On 24 October water began pouring in. After a few days, with the position at 69° 5' S, 51° 30' W, Shackleton gave the order to abandon ship, saying, "She's going down!"; and men, provisions and equipment were transferred to camps on the ice. On 21 November 1915, the wreck finally slipped beneath the surface.

Shackleton immediately sent a boat to pick up the three men from the other side of South Georgia while he set to work to organise the rescue of the Elephant Island men. His first three attempts were foiled by sea ice, which blocked the approaches to the island. He appealed to the Chilean government, which offered the use of Yelcho, a small seagoing tug from its navy. Yelcho, commanded by Captain Luis Pardo, and the British whaler SS Southern Sky reached Elephant Island on 30 August 1916, at which point the men had been isolated there for four and a half months, and Shackleton quickly evacuated all 22 men. The Yelcho took the crew first to Punta Arenas and after some days to Valparaiso in Chile where crowds warmly welcomed them back to civilisation.

When Shackleton returned to England in May 1917, Europe was in the midst of the First World War. Suffering from a heart condition, made worse by the fatigue of his arduous journeys, and too old to be conscripted, he nevertheless volunteered for the army. Repeatedly requesting posting to the front in France, he was by now drinking heavily. In October 1917, he was sent to Buenos Aires to boost British propaganda in South America. Unqualified as a diplomat, he was unsuccessful in persuading Argentina and Chile to enter the war on the Allied side. He returned home in April 1918.

Shackleton was specially appointed a temporary major on 22 July 1918. From October 1918 he served with the North Russia Expeditionary Force in the Russian Civil War under the command of Major-General (later Field Marshal Lord) Ironside, with the role of advising on the equipment and training of British forces in arctic conditions. For his "valuable services rendered in connection with Military Operations in North Russia" Shackleton was appointed an Officer of the Order of the British Empire (OBE) in the 1919 King's Birthday Honours, and was also mentioned in despatches by General Ironside. Shackleton returned to England in early March 1919, full of plans for the economic development of Northern Russia. In the midst of seeking capital, his plans foundered when Northern Russia fell to Bolshevik control. He was finally discharged from the army in October 1919, retaining his rank of major.

Shackleton returned to the lecture circuit and published his own account of the Endurance expedition, South, in December 1919. In 1920, tired of the lecture circuit, Shackleton began to consider the possibility of a last expedition. He thought seriously of going to the Beaufort Sea area of the Arctic, a largely unexplored region, and raised some interest in this idea from the Canadian government. With funds supplied by former schoolfriend John Quiller Rowett, he acquired a 125-ton Norwegian sealer, named Foca I which he renamed Quest. The plan changed; the destination became the Antarctic, and the project was defined by Shackleton as an "oceanographic and sub-antarctic expedition". The goals of the venture were imprecise, but a circumnavigation of the Antarctic continent and investigation of some "lost" sub-Antarctic islands, such as Tuanaki, were mentioned as objectives.

Rowett agreed to Finance the entire expedition, which became known as the Shackleton-Rowett Expedition. On 16 September 1921, Shackleton recorded a farewell address on a sound-on-film system created by Harry Grindell Matthews, who claimed it was the first "talking picture" ever made. The expedition left England on 24 September 1921.

Shackleton's death marked the end of the Heroic Age of Antarctic Exploration, a period of discovery characterised by journeys of geographical and scientific exploration in a largely unknown continent without any of the benefits of modern travel methods or radio communication. In the preface to his 1922 book The Worst Journey in the World, Apsley Cherry-Garrard, one of Scott's team on the Terra Nova Expedition, wrote: "For a joint scientific and geographical piece of organisation, give me Scott; for a Winter Journey, Wilson; for a dash to the Pole and nothing else, Amundsen: and if I am in the devil of a hole and want to get out of it, give me Shackleton every time".

During the ensuing decades Shackleton's status as a polar hero was generally outshone by that of Captain Scott, whose polar party had by 1925 been commemorated on more than 30 monuments in Britain alone, including stained glass windows, statues, busts and memorial tablets. A statue of Shackleton designed by Charles Sargeant Jagger was unveiled at the Royal Geographical Society's Kensington headquarters in 1932, but public memorials to Shackleton were relatively few. Likewise, the printed word saw much more attention given to Scott–a forty-page booklet on Shackleton, published in 1943 by OUP as part of a "Great Exploits" series, is described by cultural Historian Stephanie Barczewski as "a lone Example of a popular literary treatment of Shackleton in a sea of similar treatments of Scott". This disparity continued into the 1950s.

The next successful crossing of South Georgia was in October 1955, by the British Explorer Duncan Carse, who travelled much of the same route as Shackleton's party. In tribute to their achievement, he wrote: "I do not know how they did it, except that they had to — three men of the heroic age of Antarctic exploration with 50 feet of rope between them — and a carpenter's adze".

Away from his expeditions, Shackleton's life was generally restless and unfulfilled. In his search for rapid pathways to wealth and security, he launched Business ventures which failed to prosper, and he died heavily in debt. Upon his death, he was lauded in the press, but was thereafter largely forgotten, while the heroic reputation of his rival Scott was sustained for many decades. Later in the 20th century, Shackleton was "rediscovered", and rapidly became a role model for leadership as one who, in extreme circumstances, kept his team together in a survival story described by cultural Historian Stephanie Barczewski as "incredible". In his 1956 address to the British Association, Sir Raymond Priestley, one of his contemporaries, said "Scott for scientific method, Amundsen for speed and efficiency but when disaster strikes and all hope is gone, get down on your knees and pray for Shackleton", paraphrasing what Apsley Cherry-Garrard had written in a preface to The Worst Journey in the World.

In 1959 Alfred Lansing's Endurance: Shackleton's Incredible Voyage was published. This was the first of a number of books about Shackleton that began to appear, showing him in a highly positive light. At the same time, attitudes towards Scott were gradually changing as a more critical note was sounded in the literature, culminating in Roland Huntford's 1979 treatment of him in his dual biography Scott and Amundsen, described by Barczewski as a "devastating attack". This negative picture of Scott became accepted as the popular truth as the kind of heroism that Scott represented fell victim to the cultural shifts of the late twentieth century. Within a few years he was thoroughly overtaken in public esteem by Shackleton, whose popularity surged while that of his erstwhile rival declined. In 2002, in a BBC poll conducted to determine the "100 Greatest Britons", Shackleton was ranked 11th while Scott was down in 54th place.

In 1993 Trevor Potts re-enacted the Boat Journey from Elephant Island to South Georgia in honour of Sir Ernest Shackleton, totally unsupported, in a replica of the James Caird. In 2002, Channel 4 produced Shackleton, a TV serial depicting the 1914 expedition with Kenneth Branagh in the title role. Broadcast in the United States on the A&E Network, it won two Emmy Awards.

In 2001 Margaret Morrell and Stephanie Capparell presented Shackleton as a model for corporate leadership in their book Shackleton's Way: Leadership Lessons from the Great Antarctic Explorer. They wrote: "Shackleton resonates with executives in today's Business world. His people-centred approach to leadership can be a guide to anyone in a position of authority". Other management Writers were soon following this lead, using Shackleton as an exemplar for bringing order from chaos. The Centre for Leadership Studies at the University of Exeter (United Kingdom) offers a course on Shackleton, who also features in the management education programmes of several American universities. In Boston a "Shackleton School" was set up on "Outward Bound" principles, with the motto "The Journey is Everything". Shackleton has also been cited as a model leader by the US Navy, and in a textbook on Congressional leadership, Peter L Steinke calls Shackleton the archetype of the "nonanxious leader" whose "calm, reflective demeanor becomes the antibiotic warning of the toxicity of reactive behaviour". In 2001, the Athy Heritage Centre-Museum, Athy, County Kildare, Ireland, established the Ernest Shackleton Autumn School, which is held annually, to honour the memory of Ernest Shackleton.

Shackleton used his considerable fund-raising skills, and the expedition was financed largely by private donations, although the British government gave £10,000 (about £680,000 in 2008 terms). Scottish jute magnate Sir James Caird gave £24,000, Midlands industrialist Frank Dudley Docker gave £10,000 and tobacco heiress Janet Stancomb-Wills gave an undisclosed but reportedly "generous" sum. Public interest in the expedition was considerable; Shackleton received more than 5,000 applications to join it. His interviewing and selection methods sometimes seemed eccentric; believing that character and temperament were as important as technical ability, he asked unconventional questions. Thus Physicist Reginald James was asked if he could sing; others were accepted on sight because Shackleton liked the look of them, or after the briefest of interrogations. Shackleton also loosened some traditional hierarchies, expecting all men, including the Scientists, to take their share of ship's chores. He ultimately selected a crew of 56, twenty-eight on each ship.

In a Christie's auction in London in 2011, a biscuit that Shackleton gave "a starving fellow traveller" on the 1907–09 Nimrod expedition sold for £1250. That same year, on the date of what would have been Shackleton's 137th birthday, Google honored him with a Google Doodle.

In January 2013, a joint British-Australian team set out to duplicate Shackleton's 1916 trip across the Southern Ocean. Led by Explorer and environmental scientist Tim Jarvis, the team was assembled at the request of Alexandra Shackleton, Sir Ernest's granddaughter, who felt the trip would honour her grandfather's legacy. In October 2015, Shackleton's decorations and medals were auctioned; the sale raised £585,000. This team became the first to replicate the so-called "double crossing"; sailing from Elephant Island to South Georgia, and the crossing of the South Georgian mountains from King Haakon Bay (where Shackleton had landed nearly 100 years prior) to Stromness. The expedition very carefully matched legacy conditions, using a replica of the James Caird (named for the project's patron: the Alexandra Shackleton), period clothing (by Burberry), replica rations (both in calorific content and rough constitution), period navigational aids, and a Thomas Mercer chronometer just as Shackleton had used. This expedition was made into a documentary film, screening as Chasing Shackleton on PBS in the United States, and Shackleton: Death or Glory elsewhere on the Discovery Channel.

In 2016 a statue of Shackleton by Mark Richards was erected in Athy, sponsored by Kildare County Council. In 2017, the musical play Ernest Shackleton Loves Me by Val Vigoda and Joe DiPietro made its debut in New York City at the Tony Kiser Theater, an Off-Broadway venue. Blended with a parallel story of a struggling Composer, the play retells the adventure of Endurance in detail, incorporating photos and videos of the journey.