Turner was born on June 7, 1929, in Richmond, London, England, to Leonard Hugh Turner, a Journalist, and Phyllis Gregory. He had a brother, Michael (who died shortly after birth), born in 1930, and a sister, Brenda. When Turner's father died in 1932, he and his sister moved to Canada with his Canadian-born mother. The family settled in her childhood home in Rossland, British Columbia and later moved to Ottawa, Ontario.

Turner was educated at Ashbury College and St Patrick's College, Ottawa (senior matriculation). He enrolled at the University of British Columbia in 1945 at age 16, and was among Canada's outstanding track sprinters in the late 1940s, qualifying for the 1948 Olympic team. He held the Canadian record for the 100 metres, but a bad knee kept him from competing in the 1948 London Olympics. He graduated from UBC with a B.A. Honours in 1949.

Awarded a Rhodes Scholarship, Turner went on to Magdalen College at the University of Oxford, where he earned a B.A., Jurisprudence, 1951; a Bachelor of Civil Law, 1952; and an M.A., 1957. He was on the track and field team at Oxford; one of his teammates was Roger Bannister, who became the first Runner to break the four-minute barrier in the mile. At Oxford, Turner was a classmate and friend of Future Australian Prime Minister Malcolm Fraser. He also pursued doctoral studies at the University of Paris from 1952 to 1953. While attending UBC, he became a member of the fraternity Beta Theta Pi.

Turner managed to defeat the Tory incumbent in Vancouver Quadra by 3,200 votes, a surprising result given the size of the Tory wave, and became leader of the opposition. He was the only Liberal MP from British Columbia, and one of only two from west of Ontario. The Liberals, amid their worst showing in party history and led by an unpopular Turner, were said by some pundits to be following the British Liberals into oblivion. Though the Liberals had not fared much better in the 1958 election, they had clearly emerged as the main opposition party back then. After the 1984 election, however, the NDP were not far behind with 30 seats, and their leader Ed Broadbent consistently outpolled Turner and even Mulroney.

On May 19, 1959, at a party hosted by his stepfather to celebrate the opening of Government House, Turner spent a considerable amount of time dancing with Princess Margaret, one year his junior. This was the first time that Turner received significant press attention in Canada; there was considerable speculation about whether the two would become a serious couple. According to letters by Princess Margaret obtained by the Daily Mail, the relationship was more serious than previously thought with the Princess writing in one letter, seven years later, that she "nearly married him". According to contemporary press reports, the relationship caused serious consternation at Buckingham Palace as Turner is a Roman Catholic, and Margaret would have had to forfeit her place in the line of succession to the throne in order to marry him.

Turner was also generally respected for his work as a cabinet minister in the 1960s and 1970s, under prime ministers Lester Pearson and Pierre Trudeau. Colleague Walter Gordon wrote that Turner was exceptionally loyal and respectful when dealing with senior ministers in the 1960s.

Turner practised law, initially with the firm of Stikeman Elliott in Montreal, Quebec, and was elected as a Member of Parliament in 1962.

Turner was married on May 11, 1963, to Geills McCrae Kilgour (b. 1937) who was a grand-niece of Canadian Army Doctor John McCrae, the author of what is probably the best-known First World War poem, "In Flanders Fields", and sister of David Kilgour, a long-time Canadian Member of Parliament. The Turners have a daughter named Elizabeth and three sons: David, Michael, and Andrew.

In 1965, while vacationing in Barbados, Turner noticed that former prime minister and Leader of the Opposition John Diefenbaker, staying at the same hotel, was struggling in the strong surf and undertow and Turner, being a competitive Swimmer during university days, jumped in and pulled Diefenbaker to shore.

He served in the Cabinet of Prime Minister Lester Pearson in various capacities, most notably as Minister of Consumer and Corporate Affairs. When Pearson retired, Turner ran to succeed him at the 1968 leadership convention. Turner, at age 38 the youngest of the dozen leadership candidates, stated "My time is now", and remarked during his speech that he was "not here for some vague, Future convention in say, 1984". Turner stayed on until the fourth and final ballot, finishing third behind Pierre Trudeau and runner-up Robert Winters.

Early in the campaign, Turner appeared rusty and old fashioned. His policies contrasted with Trudeau and seemed to legitimize the Tory calls for lowering the deficit, improving relations with the United States, cutting the bureaucracy, and promoting more federal-provincial harmony. He spoke of creating "make work programs", a discarded phrase from the 1970s that had been replaced by the less patronizing "job creation programs". Turner was also caught on television patting the bottoms of Liberal Party President Iona Campagnolo and Vice-President Lise St. Martin-Tremblay, causing an uproar among feminists, who saw such behaviour as sexist and condescending.

Turner then served as Minister of Finance from 1972 until 1975. His challenges were severe in the face of global financial issues such as the explosive increase in the price of oil, collapse of the postwar trading system, slowing economic growth, soaring inflation, and growing deficits. His positions were more conservative than Trudeau's and they drew apart. In 1975 Turner surprisingly resigned from cabinet, reportedly due to personality conflicts with Trudeau. The Liberals had won the 1974 election by attacking Robert Stanfield's Progressive Conservatives over their platform involving wage and price controls. However, Trudeau decided to implement the wage and price controls in late 1975, so some have suggested that Turner quit rather than carry out that proposal. In a 2013 interview with Catherine Clark on CPAC Turner confirmed his resignation from cabinet was a direct result of refusing to implement wage and price controls, after campaigning against them in 1974.

From 1975 to 1984, Turner worked as a corporate Lawyer at Bay Street law firm McMillan Binch. When Pierre Trudeau resigned as Liberal leader in 1979 following an election loss, Turner announced that he would not be a candidate for the Liberal leadership. Trudeau was talked into rescinding his resignation after the government of Joe Clark was defeated by a motion of no confidence, and returned to contest and win the 1980 federal election. Trudeau would serve as Prime Minister until 1984.

Turner discovered late in the campaign that the Liberals' electoral hopes were poor in their traditional stronghold of Quebec. The party had previously relied on Trudeau's appeal, patronage, and traditional dislike of the Progressive Conservatives for victory in recent elections. Turner had surrounded himself with Trudeau's factional opponents and Trudeau himself did not endorse Turner. In a last-minute turnaround, Turner rehired much of Trudeau's staff during the final weeks, but this had little effect. Quebec's disaffection with the federal Liberals regarding the patriation of constitution in 1982 further contributed to their defeat. Mulroney, a native Quebecker, was able to harness that discontent to the Progressive Conservatives' advantage by promising a new constitutional agreement.

Turner campaigned much more vigorously than in 1984, rallying support against the proposed FTA, an agreement that he said would lead to the abandonment of Canada's political sovereignty to the United States. His performance in the debate and his attacks on Mulroney and the FTA, where he accused the Progressive Conservative Prime Minister of "selling Canada out with one signature of a pen", raised his poll numbers, and soon the Liberals were hoping for a majority. This prompted the Progressive Conservatives to stop the relatively calm campaign they had been running, and go with Allan Gregg's suggestion of "bombing the bridge" that joined anti-FTA voters and the Liberals: Turner's credibility. The ads focused on Turner's leadership struggles, and combined with over $6 million in pro-FTA ads, stopped Turner's momentum. Also not helping the Liberals was that the NDP had opposed the FTA as well (though not as vocally); this likely resulted in vote-splitting between the opposition parties. Although most Canadians voted for parties opposed to free trade, the Tories were returned with a majority government, and implemented the deal.

Turner's leadership was frequently questioned, and in the lead up to the 1986 Liberal convention, a vote of confidence loomed large. The popular Chrétien resigned his seat, creating a stir in caucus. The ongoing and often open unpopularity of Turner within his own party led to many editorial cartoonists drawing him with a back stabbed full of knives. Keith Davey and other Liberals began a public campaign against Turner, coinciding with backroom struggles involving Chrétien's supporters. The public conflict is said to have influenced many Liberals to support Turner, and he ended up getting 75% of the delegate vote.

When the election was called in 1988, the Liberals had some early struggles, notably during one day in Montreal where 3 different costs were given for the proposed Liberal daycare program. The campaign was also hampered by a Canadian Broadcasting Corporation report that stated there was a movement in the backroom to replace Turner with Chrétien.

The election loss seemed to confirm Turner's fate; he announced he was standing down from the party leadership in May 1989, officially resigning in June 1990. Turner resigned as Official Opposition leader, while still holding the Liberal leadership, so Herb Gray became the caucus leader for the interim. Chrétien won that year's leadership convention over Paul Martin. Although not officially endorsed by Turner himself, Martin was widely the favourite of Turner's supporters.

Turner continued to represent Vancouver Quadra in the House of Commons for another few years as a backbencher before retiring from politics in the 1993 election.

Turner was appointed a Companion of the Order of Canada on October 19, 1994, and was invested on May 3, 1995. His citation reads:

Turner was ranked No. 18 out of the first 20 Prime Ministers of Canada (through Jean Chrétien) by a survey of Canadian historians in 1999. The survey was used in the book Prime Ministers: Ranking Canada's Leaders by J. L. Granatstein and Norman Hillmer.

In late 2004, Turner headed the delegation of Canadian election monitors to Ukraine who helped monitor the Ukrainian presidential runoff vote of December 26. The monitoring was the first mission of the new Canada Corps.

Turner, along with other former prime ministers, has taken part in the reality series Canada's Next Great Prime Minister. He was intending on taking part during the 2007 edition, but due to illness, had to be replaced at the last minute by Paul Martin. Turner's health had recovered sufficiently for him to participate in the 2008 edition of the show. He is the oldest living former Canadian prime minister.

The Centre for the Study of Democracy at Queen's University produced in 2008 a revised and updated 40th anniversary edition of selected Turner speeches and writings, entitled Politics with Purpose, published by McGill-Queen's University Press; the book had been published originally in 1968. Turner's career was honoured by CSD in a special day-long tribute at Queen's on October 24, 2008.

The last days of the campaign saw one Liberal blunder piled upon another. Turner continued to make gaffes that caused voters to see him as incompetent and a relic from the past. On September 4, the Liberals were swept from power in a Tory landslide. The Liberals were cut down to 40 seats, the fewest in the party's history until 2011, against 211 for the Progressive Conservatives. The Liberals had fallen to 17 seats in Quebec, all but four in and around Montreal. Eleven members of Turner's cabinet were defeated. At the time, it was the worst defeat ever suffered for a governing party in the federal parliament.

The Liberals faced more internal conflict in the next few years, but polls frequently had them in front of the Progressive Conservatives (however, with Turner last in preferred prime minister categories). The upcoming Canada–US Free Trade Agreement and Meech Lake Accord threatened to divide the party until Turner took the position of being pro-Meech Lake and against the FTA. Turner asked the Liberal Senators to hold off on passing the legislation to implement the agreement until an election was held. It was later revealed that Mulroney planned to have an election called, anyway.

During the televised leaders' debate, Turner attacked Mulroney over the patronage machine that the latter had allegedly set up in anticipation of victory, comparing it to the Union Nationale governments of Quebec. Mulroney responded by pointing to the raft of patronage appointments made on the advice of Trudeau and Turner. Turner had the right to advise Sauvé to cancel Trudeau's appointments—advice that she was bound to follow by convention—but failed to do so and added to his own. Mulroney demanded that Turner apologize to the country for what he called "these horrible appointments." Turner claimed that "I had no option" except to let them stand. Mulroney responded, "You had an option, sir – to say 'no' – and you chose to say 'yes' to the old attitudes and the old stories of the Liberal Party." He highlighted the Liberals long record in government and resulting patronage appointments. Many observers believed that Mulroney clinched the election at this point, as it made Turner look weak and indecisive. Analysts agreed he was "done in by television."