William Lyon Mackenzie King

King was especially concerned with issues of social welfare and was influenced by the settlement house movement pioneered by Toynbee Hall in London, England. He played a central role in fomenting a students' strike at the university in 1895. He was in close touch, behind the scenes, with Vice-Chancellor William Mulock, for whom the strike provided a chance to embarrass his rivals Chancellor Edward Blake and President James Loudon. King failed to gain his immediate objective, a teaching position at the University, but earned political credit with Mulock, the man who would invite him to Ottawa and make him a deputy minister only five years later. While studying at the University of Toronto, King also contributed to the campus newspaper The Varsity.

King earned five university degrees. He obtained three degrees from the University of Toronto: BA 1895, LLB 1896, and MA 1897; he earned his LLB in 1896 from Osgoode Hall Law School. While studying in Toronto he met a wide circle of friends, many of whom became prominent. He was an early member and officer of the Kappa Alpha Society, which included a number of these individuals (two future Ontario Supreme Court Justices and the future Chairman of the University itself). It encouraged debate on political ideas. He also met Arthur Meighen, a future political rival; the two men did not get on especially well from the start.

After studying at the University of Chicago and working with Jane Addams at her settlement house, Hull House, King proceeded to Harvard University. He earned an MA in political economy from Harvard in 1898. In 1909, Harvard granted him a PhD for a dissertation on Oriental Immigration to Canada. It was a report he had written while he was Deputy-Minister of Labour in 1908. In it he argued against the immigration of Asians, saying:

King was appointed in 1900 as Deputy Minister at the head of the Canadian government's new department of Labour, and became active in policy domains from Japanese immigration to railways, notably the Industrial Disputes Investigations Act (1907) which sought to avert labour strikes by prior conciliation.

In 1901, King's roommate and best friend, Henry Albert Harper, died heroically during a skating party when a young woman fell through the ice of the partly frozen Ottawa River. Harper dove into the water to try to save her, and perished in the attempt. King led the effort to raise a memorial to Harper, which resulted in the erection of the Sir Galahad statue on Parliament Hill in 1905. In 1906, King published a memoir of Harper, entitled The Secret of Heroism.

While Deputy Minister of Labour, King was appointed to investigate the causes of and claims for compensation resulting from the 1907 Asiatic Exclusion League riots in Vancouver's Chinatown and Japantown. One of the claims for damages came from Chinese opium dealers, which led King to investigate narcotics use in Vancouver, British Columbia. Following the investigation King reported that white women were also opium users, not just Chinese men, and the federal government used the report to justify the first legislation outlawing narcotics in Canada. The report failed to include any reference regarding the Opium Wars, the involvement of the East Indian Trading company, or the official Chinese government's resistance to the opium trade which was renewed on September 20, 1906.

He was first elected to Parliament as a Liberal in a 1908 by-election, and then in 1909 was appointed as the first-ever Minister of Labour.

King expanded the Department of External Affairs, founded in 1909, to further promote Canadian autonomy from Britain. The new department took some time to develop, but over time it significantly increased the reach and projection of Canadian diplomacy. Prior to this, Canada had relied on British diplomats who owed their first loyalty to London. King recruited many high-calibre people for the new venture, including future prime minister Lester Pearson and influential career administrators Norman Robertson and Hume Wrong. This project was a key element of his overall strategy, setting Canada on a course independent of Britain, of former colonizer France, as well as of the neighbouring powerful United States.

King's term as Minister of Labour was marked by two significant achievements. He led the passage of the Industrial Disputes Investigation Act and the Combines Investigation Act, which he had shaped during his civil and parliamentary service. The legislation significantly improved the financial situation for millions of Canadian workers. He lost his seat in the 1911 general election, which saw the Conservatives defeat his Liberals.

After his defeat, King went on the lecture circuit on behalf of the Liberal Party. In June 1914 John D. Rockefeller Jr. hired him at the Rockefeller Foundation in New York City, to head its new Department of Industrial Research. It paid $12,000 per year, compared to the meagre $2,500 per year the Liberal Party was paying. He worked for the Foundation until 1918, forming a close working association and friendship with Rockefeller, advising him through the turbulent period of the 1913-1914 Strike and Ludlow Massacre–in what is known as the Colorado Coalfield War–at a family-owned coal company in Colorado, which subsequently set the stage for a new era in labour management in America. King became one of the earliest expert practitioners in the emerging field of industrial relations.

In 1917, Canada was in crisis; King supported Liberal leader Sir Wilfrid Laurier in his opposition to conscription, which was violently opposed in the province of Quebec. The Liberal party became deeply split, with most Anglophones joining in the pro-conscription Union government, a coalition controlled by the Conservatives under Prime Minister Sir Robert Borden. King returned to Canada to run in the 1917 election, which focused almost entirely on the conscription issue. Unable to overcome a landslide against Laurier, King lost in the constituency of North York, which his grandfather had once represented.

In 1918, King, assisted by his friend F. A. McGregor, published the far-sighted book Industry and Humanity: A Study in the Principles Underlying Industrial Reconstruction, a dense, abstract work he wrote in response to the Ludlow massacre. It went over the heads of most readers, but revealed the practical idealism behind King's political thinking. He emphasized that capital and labour were natural allies, not foes, and that the community at large (represented by the government) should be the third and decisive party in industrial disputes. He expressed derision for syndicates and trades unions, chastising them for aiming at the "destruction by force of existing organization, and the transfer of industrial capital from the present possessors" to themselves.

Quitting the Rockefeller Foundation in February 1918, King became an independent consultant on labour issues for the next two years, earning $1,000 per week from leading American corporations. Even so, he kept his official residence in Ottawa, hoping for a call to duty.

King was Laurier's chosen successor as leader of the Liberal Party, but it was deeply divided by Quebec's total opposition to conscription and the agrarian revolt in Ontario and the Prairies. Levin argues that when King returned to politics in 1919, he was a rusty outsider with a weak base facing a nation bitterly split by language, regionalism and class. He outmaneuvered more senior competitors by embracing Laurier's legacy, championing labour interests, calling for welfare reform, and offering solid opposition to the Conservative enemy. When Laurier died in 1919, King was elected leader in the first Liberal leadership convention, defeating his four rivals on the fourth ballot. He won thanks to the support of the Quebec bloc, organized by his long-time lieutenant in Quebec, Ernest Lapointe (1876–1941). King could not speak French and had minimal interest in Quebec, but in election after election for the next 20 years (save for 1930), Lapointe produced the critical seats to give the Liberals control of the Commons. He was almost co-Prime Minister with King until his death in 1941.

Once he became the Liberal leader in 1919 he paid closer attention to the Prairies, a fast-developing region. With a highly romanticized view he envisioned the pioneers as morally sound, hardworking individuals who lived close to nature and to God. The reform ferment in the region meshed with his self-image as a social reformer and fighter for the "people" against the "interests". Viewing a glorious sunrise in Alberta in 1920, he wrote in his diary, "I thought of the New Day, the New Social Order. It seems like Heaven's prophecy of the dawn of a new era, revealed to me." Pragmatism played a role as well, since his party depended for its survival on the votes of Progressive Party members of parliament who represented farmers in Ontario and the Prairies. He convinced many Progressives to return to the Liberal fold.

In the 1921 election, his party defeated Arthur Meighen and the Conservatives, and he became Prime Minister. King's Liberals originally had a bare majority position, however, since they had won 118 out of 235 seats, exactly the minimum for a majority. The Conservatives won 49, the newly formed Progressive Party won 58 (but declined to form the official Opposition), and the remaining ten seats went to fringe parties and Independents; most of these ten supported the Progressives.

As Prime Minister of Canada, King was appointed to the Privy Council of the United Kingdom on 20 June 1922 and was sworn at Buckingham Palace on 11 October 1923, during the 1923 Imperial Conference.

During his first term of office, from 1921 to 1926, King pursued a conservative domestic policy with the object of lowering wartime taxes and, especially, wartime ethnic and labour tensions. "The War is over", he argued, "and for a long time to come it is going to take all that the energies of man can do to bridge the chasm and heal the wounds which the War has made in our social life." He sought a Canadian voice independent of London in foreign affairs. In September 1922 the British Prime Minister, David Lloyd George, appealed repeatedly to King for Canadian support in the Chanak crisis, in which a war threatened between Britain and Turkey. King coldly replied that the Canadian Parliament would decide what policy to follow, making clear it would not be bound by London's suggestions; the crisis soon dissipated, but the episode led to the downfall of Lloyd George.

In 1923, King government passed the Chinese Immigration Act, 1923 banning most forms of Chinese immigration to Canada. Immigration from most countries was controlled or restricted in some way, but only the Chinese were so completely prohibited from immigrating. This was after various members of the federal and some provincial governments (especially British Columbia) put pressure on the federal government to discourage Chinese immigration.

King called an election in 1925, in which the Conservatives won the most seats, but not a majority in the House of Commons. King held onto power with the support of the Progressives. A corruption scandal discovered late in his first term involved misdeeds around the expansion of the Beauharnois Canal in Quebec; this led to extensive inquiries and eventually a Royal Commission, which exposed the Beauharnois Scandal. The resulting press coverage damaged King's party in the election. Early in his second term, another corruption scandal, this time in the Department of Customs, was revealed, which led to more support for the Conservatives and Progressives, and the possibility that King would be forced to resign, if he lost sufficient support in the Commons. King had no personal connection to this scandal, although one of his own appointees was at the heart of it. Opposition leader Meighen unleashed his fierce invective towards King, stating he was hanging onto power "like a lobster with lockjaw".`

In 1926, King, facing a House of Commons vote connected to the customs scandal that could force his government to resign, advised the Governor General, Lord Byng, to dissolve Parliament and call another election. Byng, however, declined the Prime Minister's request – the first time in Canadian history that a request for dissolution was refused; and, to date, the only time the governor general of Canada has done so. (The most recent refusal of dissolution in Canada was in 2017 when the lieutenant governor of British Columbia declined a request by the premier.) Byng instead asked Leader of the Opposition, Arthur Meighen, to form government. Although the Conservatives held the most seats within parliament, they did not control a majority and were soon themselves defeated on a motion of confidence. Meighen then had to again request a dissolution of Parliament, which Byng now granted.

His government was in power during the beginning of the Great Depression, but was slow to respond to the mounting crisis. He felt that the crisis was a temporary swing of the business cycle and that the economy would soon recover without government intervention. Critics said he was out of touch. Just prior to the election, King carelessly remarked that he "would not give a five-cent piece" to Tory provincial governments for unemployment relief. The opposition made this remark a catch-phrase; the main issue was the deterioration in the economy and whether the prime minister was out of touch with the hardships of ordinary people. The Liberals lost the election of 1930 to the Conservative Party, led by Richard Bedford Bennett. The popular vote was very close between the two parties, with the Liberals actually earning more votes than in 1926, but the Conservatives had a geographical advantage that turned into enough seats to give a majority.

In domestic affairs King strengthened the Liberal policy of increasing the powers of the provincial governments by transferring to the governments of Manitoba, Alberta, and Saskatchewan the ownership of the crown lands within those provinces, as well as the subsoil rights; these in particular would become increasingly important, as petroleum and other natural resources proved very abundant. In collaboration with the provincial governments, he inaugurated a system of old-age pensions based on need. In February 1930, he appointed Cairine Wilson as the first female senator in Canadian history.

King therefore went to the Imperial Conference of 1926 and argued for greater autonomy of the Dominions. This resulted in the Balfour Declaration 1926, which announced the equal status of all members of the British Commonwealth (as it was known then), including Britain. This eventually led to the Statute of Westminster 1931. The Canadian city of Hamilton hosted the first Empire Games in 1930; this competition later became known as the Commonwealth Games, and is held every four years.

After his loss, King stayed on as Opposition Leader, where it was his policy to refrain from offering advice or alternative policies. Indeed, his policy preferences were not much different from Bennett's, and he let the Conservative government have its way. Though he gave the impression of sympathy with progressive and liberal causes, he had no enthusiasm for the New Deal of American President Franklin D. Roosevelt (which Bennett eventually tried to emulate, after floundering without solutions for several years), and he never advocated massive government action to alleviate depression in Canada. Upon his return to office in October 1935, however, King seemed to demonstrate a commitment (like Franklin Roosevelt) to the underprivileged, speaking of a new era where "poverty and adversity, want and misery are the enemies which Liberalism will seek to banish from the land".

In the 1935 election the Liberals used the slogan "King or Chaos" to win a landslide victory. For the first time in his political career, King led an undisputed Liberal majority government. Promising a much-desired trade treaty with the U.S., the King government passed the 1935 Reciprocal Trade Agreement. It marked the turning point in Canadian-American economic relations, reversing the disastrous trade war of 1930–31, lowering tariffs, and yielding a dramatic increase in trade. More subtly, it revealed to the prime minister and President Roosevelt that they could work together well.

Some historians have interpreted passages in his diaries as suggesting that King regularly had sexual relations with prostitutes. Others, also basing their claims on passages of his diaries, have suggested that King was in love with Lord Tweedsmuir, whom he had chosen for appointment as Governor General in 1935.

The worst of the Depression had passed by 1935 when King regained power. He implemented relief programs such as the National Housing Act and National Employment Commission. His government also established the Canadian Broadcasting Corporation in 1936, Trans-Canada Air Lines (the precursor to Air Canada) in 1937, and the National Film Board of Canada in 1939. In 1938, his government nationalised the Bank of Canada into a Crown corporation.

After 1936 the prime minister lost patience when western Canadians preferred radical alternatives such as the CCF (Co-operative Commonwealth Federation) and Social Credit to his middle-of-the-road liberalism. Indeed, he came close to writing off the region with his comment that the prairie dust bowl was "part of the U.S. desert area. I doubt if it will be of any real use again." Instead he paid more attention to the industrial regions and the needs of Ontario and Quebec, particularly with respect to the proposed St. Lawrence Seaway project with the United States. As for the unemployed, he was hostile to federal relief, and only reluctantly accepted a Keynesian solution that involved federal deficit spending, tax cuts and subsidies to the housing market.

In March 1936, in response to the German remilitarization of the Rhineland, King had the Canadian High Commissioner in London inform the British government that if Britain went to war with Germany over the Rhineland issue, Canada would remain neutral. In June 1937, during an Imperial Conference of all the Dominion Prime Ministers in London, King informed British Prime Minister Neville Chamberlain that Canada would only go to war if Britain were directly attacked, and that if Britain were to become involved in a continental war then Chamberlain was not to expect Canadian support.

In 1937, King visited Germany and met with Adolf Hitler. Possessing a religious yearning for direct insight into the hidden mysteries of life and the universe, and strongly influenced by the operas of Richard Wagner (who was also Hitler's favourite composer), King decided Hitler was akin to mythical Wagnerian heroes within whom good and evil were struggling. He thought that good would eventually triumph and Hitler would redeem his people and lead them to a harmonious, uplifting future. These spiritual attitudes not only guided Canada's relations with Hitler but gave the prime minister the comforting sense of a higher mission, that of helping to lead Hitler to peace. King commented in his journal that "he is really one who truly loves his fellow-men, and his country, and would make any sacrifice for their good". He forecast that "the world will yet come to see a very great man–mystic in Hitler ... I cannot abide in Nazism – the regimentation – cruelty – oppression of Jews – attitude towards religion, etc., but Hitler ... will rank some day with Joan of Arc among the deliverers of his people."

In late 1938, during the great crisis in Europe over Czechoslovakia that culminated in the Munich Agreement, Canadians were divided. Francophones insisted on neutrality, as did some top advisers like Oscar D. Skelton. Imperialists stood behind Britain and were willing to fight Germany. King, who served as his own secretary of state for external affairs (foreign minister), said privately that if he had to choose he would not be neutral, but he made no public statement. All of Canada was relieved that the British appeasement at Munich, while sacrificing the rights of Czechoslovakia, seemed to bring peace.

As British Prime Minister Neville Chamberlain "negotiated in Munich with Adolf Hitler in September 1938, Mackenzie King, Canada’s Prime Minister, grew agitated." King realized the likelihood of World War II and began mobilizing on August 25, 1939, with full mobilization on September 1, 1939, the day Germany invaded Poland. In 1914, Canada was at war by virtue of King George V's declaration. In 1939, the Prime Minister asserted Canada's autonomy and convened the House of Commons on September 7, nearly a month ahead of schedule, to discuss the government's intention to enter the war, which was approved two days later. On September 10, Prime Minister King, through his high commissioner in London, issued a request to King George VI, asking him, in his capacity as King of Canada, to declare Canada at war against Germany.

Over the next fourteen years, a wide range of reforms similar to those association with the New Deal were realized during Mackenzie King's last period in office as Prime Minister. In 1939, compulsory contributions for pensions for low-income widows and orphans were introduced (although these only covered the regularly employed) while depressed farmers were subsidized from that same year onwards. In 1944, family allowances were introduced, and from 1948 the federal government subsidized medical services in the provinces. The various provinces were assisted by the Federal Unemployment and Agricultural Assistance Act of 1938 and the Youth Training Act of 1939 to create training programs for young persons, while an amendment to the Criminal Code (which received Royal assent in May 1939) provided against refusal to hire, or dismissal, "solely because of a person's membership in a lawful trade-union or association". In 1937, the age for blind persons to qualify for old-age pensions was reduced to 40 in 1937, and later to 21 in 1947.

Under King's administration, the Canadian government, responding to strong public opinion, especially in Quebec, refused to expand immigration opportunities for Jewish refugees from Europe. In June 1939 Canada, along with Cuba and the United States, refused to allow entry for the 900 Jewish refugees aboard the passenger ship MS St. Louis.

To re-arm Canada he built the Royal Canadian Air Force as a viable military power, while at the same time keeping it separate from Britain's Royal Air Force. He was instrumental in obtaining the British Commonwealth Air Training Plan Agreement, which was signed in Ottawa in December 1939, binding Canada, Britain, New Zealand and Australia to a program that eventually trained half the airmen from those four nations in the Second World War.

King's promise not to impose conscription contributed to the defeat of Maurice Duplessis's Union Nationale Quebec provincial government in 1939 and the Liberals' re-election in the 1940 election. But after the fall of France in 1940, Canada introduced conscription for home service. Still, only volunteers were to be sent overseas. King wanted to avoid a repeat of the Conscription Crisis of 1917. By 1942, the military was pressing King hard to send conscripts to Europe. In 1942, King held a national plebiscite on the issue, asking the nation to relieve him of the commitment he had made during the election campaign. In the House of Commons on June 10, 1942, he said that his policy was "not necessarily conscription but conscription if necessary".

In the lead-up to World War II in 1939, King affirmed Canadian autonomy by saying that the Canadian Parliament would make the final decision on the issue of going to war. He reassured the pro-British Canadians that Parliament would surely decide that Canada would be at Britain's side if Great Britain was drawn into a major war. At the same time, he reassured those who were suspicious of British influence in Canada by promising that Canada would not participate in British colonial wars. His Quebec lieutenant, Ernest Lapointe, promised French-Canadians that the government would not introduce conscription; individual participation would be voluntary. In 1939, in a country which had seemed deeply divided, these promises made it possible for Parliament to agree almost unanimously to declare war.

King linked Canada more and more closely to the United States, signing an agreement with Roosevelt at Ogdensburg, New York in August 1940 that provided for the close cooperation of Canadian and American forces, despite the fact that the U.S. remained officially neutral until the bombing of Pearl Harbor on December 7, 1941. During the war the Americans took virtual control of the Yukon and the then-British colony of Newfoundland in building the Alaska Highway and major airbases.

Following the Attack on Pearl Harbor in December 1941, Japanese Canadians were categorized as enemy aliens under the War Measures Act, which began to remove their personal rights. Starting on December 8, 1941, 1,200 Japanese-Canadian-owned fishing vessels were impounded as a "defence measure." On January 14, 1942, the federal government passed an order calling for the removal of male Japanese nationals between 18 and 45 years of age from a designated protected area of 100 miles inland from the British Columbia coast, enacted a ban against Japanese-Canadian fishing during the war, banned shortwave radios and controlled the sale of gasoline and dynamite to Japanese Canadians. Japanese nationals removed from the coast after the January 14 order were sent to road camps around Jasper, Alberta. Three weeks later, on February 19, 1942, US President Franklin D. Roosevelt signed Executive Order 9066, which called for the removal of 110,000 people of Japanese ancestry from the American coastline. A historian of internment, Ann Sunahara, argues that "the American action sealed the fate of Japanese Canadians." On February 24, the federal government passed order-in-council PC 1468 which allowed for the removal of "all persons of Japanese origin" This order-in-council allowed the Minister of Justice the broad powers of removing people from any protected area in Canada, but was meant for Japanese Canadians on the Pacific coast in particular. On February 25, the federal government announced that Japanese Canadians were being moved for reasons of national security. In all, some 27,000 people were detained without charge or trial, and their property confiscated. Others were deported to Japan. King and his Cabinet ignored reports from the Royal Canadian Mounted Police and Canadian military that most of the Japanese were law-abiding and not a threat. Major General Ken Stuart told Ottawa, "I cannot see that the Japanese Canadians constitute the slightest menace to national security." King's political direction on this issue closely followed postulates from his 1909 doctoral thesis at Harvard.

French Canadians voted against conscription, with over 70% opposed, but an overwhelming majority – over 80% – of English Canadians supported it. French and English conscripts were sent to fight in the Aleutian Islands in 1943 – technically North American soil and therefore not "overseas" – but the mix of Canadian volunteers and draftees found that the Japanese troops had fled before their arrival. Otherwise, King continued with a campaign to recruit volunteers, hoping to address the problem with the shortage of troops caused by heavy losses in the Dieppe Raid in 1942, in Italy in 1943, and after the Battle of Normandy in 1944. In November 1944, the Government decided it was necessary to send conscripts to Europe for the war. This led to a brief political crisis (see Conscription Crisis of 1944) and a mutiny by conscripts posted in British Columbia, but the war ended a few months later. Over 15,000 conscripts went to Europe, though only a few hundred saw combat.

During the war, Canada rapidly expanded its diplomatic missions abroad. However British Prime Minister Winston Churchill made all the major military and diplomatic decisions for Canada and the other dominions, with minimal consultation. While Canada hosted two major Allied conferences in Quebec in 1943 and 1944, neither Mackenzie King nor his senior generals and admirals were invited to take part in any of the discussions.

The Federal Home Improvement Plan of 1937 provided subsidized rates of interest on rehabilitation loans to 66,900 homes, while the National Housing Act of 1938 made provision for the building of low-rent housing. Another Housing Act was later passed in 1944 with the intention of providing federally guaranteed loans or mortgages to individuals who wished to repair or construct dwellings through their own initiative. The Vocational Training Co-ordination Act of 1942 provided an impetus to the provinces to set up facilities for postsecondary vocational training, and in 1948 the Industrial Relations and Disputes Investigation Act was passed, which safeguarded the rights of workers to join unions while requiring employers to recognize unions chosen by their employees.

King's government greatly expanded the role of the National Research Council of Canada during the war, moving into full-scale research in nuclear physics and commercial use of nuclear power in the following years. King, with C. D. Howe acting as point man, moved the nuclear group from Montreal to Chalk River, Ontario in 1944, with the establishment of Chalk River Nuclear Laboratories and the residential town of Deep River, Ontario. Canada became a world leader in this field, with the NRX reactor becoming operational in 1947; at the time, NRX was the only operational nuclear reactor outside the United States. The NRC also contributed to wartime scientific development in other ways during this period.

With the war winding down, King held a federal election in 1945 and won a minority, but formed a functioning coalition to continue governing. As King was defeated in his own riding of Prince Albert, fellow Liberal William MacDiarmid, who was re-elected in the safe seat of Glengarry, resigned so that a by-election could be held, which was subsequently won by King.

King helped found the United Nations in 1945 and attended the opening meetings in San Francisco. However, he became pessimistic about the organization's future possibilities. After the war, King quickly dismantled wartime controls. Unlike World War I, press censorship ended with the hostilities. He began an ambitious program of social programs and laid the groundwork for Newfoundland's later entry into Canada.

King moved Canada into the deepening Cold War in alliance with the U.S. and Britain. He dealt with the espionage revelations of Soviet cipher clerk Igor Gouzenko, who defected in Ottawa in September 1945, by quickly appointing a Royal Commission to investigate Gouzenko's allegations of a Canadian Communist spy-ring transmitting top-secret documents to Moscow. External Affairs Minister Louis St. Laurent dealt decisively with this crisis, the first of its type in Canada's history. St. Laurent's leadership deepened King's respect, and helped make St. Laurent the next Canadian Prime Minister three years later.

King's government introduced the Canadian Citizenship Act in 1946, which officially created the notion of "Canadian citizens". Prior to this, Canadians were considered British subjects living in Canada. On January 3, 1947, King received Canadian citizenship certificate number 0001.

On January 20, 1948, King called on the Liberal Party to hold its first national convention since 1919 to choose a new leader. The August convention chose St. Laurent as the new leader of the Liberal Party. Three months later, King retired after 22 years as prime minister. King also had the most terms (six) as Prime Minister. Sir John A. Macdonald was second-in-line, with 19 years, as the longest-serving Prime Minister in Canadian history (1867–1873, 1878–1891). King was not charismatic and did not have a large personal following. Only eight Canadians in 100 picked him when the Canadian Gallup (CIPO) poll asked in September 1946, "What person living in any part of the world today do you admire?" Nevertheless, his Liberal Party was easily re-elected in the election of 1945.

King died on July 22, 1950, at his country estate in Kingsmere from pneumonia, with his retirement plans to write his memoirs unfulfilled. He is buried in Mount Pleasant Cemetery, Toronto.

Scholars attribute King's long tenure as party leader to his wide range of skills that were appropriate to Canada's needs. King kept a very candid diary from 1893, when he was still an undergraduate, until a few days before his death in 1950; the volumes, stacked in a row, span a length of over seven metres and comprise over 50,000 manuscript pages of typed transcribed text. One biographer called these diaries "the most important single political document in twentieth-century Canadian history," for they explain motivations of the Canadian war efforts and describe other events in detail.

He was named a Person of National Historic Significance in 1968.

Historians have seen in his spiritualism and occult activities a penchant for forging unities from antitheses, thus having latent political import. Historian C.P. Stacey, in his 1976 book A Very Double Life examined King's secret life in detail, argued that King did not allow his beliefs to influence his decisions on political matters. Stacey wrote that King entirely gave up his interests in the occult and spiritualism during World War II.

On September 22, 1988, Prime Minister Brian Mulroney delivered an apology for the internment, and the Canadian government announced a compensation package.

In 1998, there was controversy over King's exclusion from a memorial to the Quebec Conference, which was attended by King, Roosevelt, and Churchill. The monument was commissioned by the sovereigntist Parti Québécois government of Quebec, which justified the decision on their interpretation that King was acting merely as a host for the meeting between Roosevelt and Churchill. Canadian federalists, however, accused the government of Quebec of trying to advance their own political agenda.