The 1957 Canadian federal election was held June 10, 1957, to select the 265 members of the House of Commons of Canada of the 23rd Parliament of Canada. In one of the greatest upsets in Canadian political history, the Progressive Conservative Party (also known as "PCs" or "Tories"), led by John Diefenbaker, brought an end to 22 years of Liberal rule, as the Tories were able to form a minority government despite losing the popular vote to the Liberals.

The Liberal Party had governed Canada since 1935, winning five consecutive elections. Under Prime Ministers William Lyon Mackenzie King and Louis St. Laurent, the government gradually built a welfare state. During the Liberals' fifth term in office, the opposition parties depicted them as arrogant and unresponsive to Canadians' needs. Controversial events, such as the 1956 "Pipeline Debate" over the construction of the Trans-Canada Pipeline, had hurt the government. St. Laurent, nicknamed "Uncle Louis", remained popular, but exercised little supervision over his cabinet ministers.

In 1956, Tory leader George A. Drew unexpectedly resigned due to ill health. In his place, the PC party elected the fiery and charismatic Diefenbaker. The Tories ran a campaign centred on their new leader, who attracted large crowds to rallies and made a strong impression on television. The Liberals ran a lacklustre campaign, and St. Laurent made few television appearances. Uncomfortable with the medium, the Prime Minister read his speeches from a script and refused to wear makeup.

Abandoning their usual strategy of trying to make major inroads in Liberal-dominated Quebec, the Tories focused on winning seats in the other provinces. They were successful; though they gained few seats in Quebec, they won 112 seats overall to the Liberals' 105. With the remaining seats won by other parties, the PC party only had a plurality in the House of Commons, but the margin was sufficient to make John Diefenbaker Canada's first Tory Prime Minister since R. B. Bennett in 1935.

John George Diefenbaker (; September 18, 1895 – August 16, 1979) was the 13th prime minister of Canada, serving from 1957 to 1963. He was the only Progressive Conservative party leader between 1930 and 1979 to lead the party to an election victory, doing so three times, although only once with a majority of the seats in the House of Commons.

Diefenbaker was born in southwestern Ontario in the small town of Neustadt in 1895. In 1903, his family migrated west to the portion of the North-West Territories which would soon become the province of Saskatchewan. He grew up in the province and was interested in politics from a young age. After service in World War I, Diefenbaker became a noted criminal defence lawyer. He contested elections through the 1920s and 1930s with little success until he was finally elected to the House of Commons in 1940.

Diefenbaker was repeatedly a candidate for the party leadership. He gained that position in 1956, on his third attempt. In 1957, he led the party to its first electoral victory in 27 years; a year later he called a snap election and spearheaded them to one of their greatest triumphs. Diefenbaker appointed the first female minister in Canadian history to his cabinet (Ellen Fairclough), as well as the first Indigenous member of the Senate (James Gladstone). During his six years as prime minister, his government obtained passage of the Canadian Bill of Rights and granted the vote to the First Nations and Inuit peoples. In 1962, Diefenbaker's government eliminated racial discrimination in immigration policy. In foreign policy, his stance against apartheid helped secure the departure of South Africa from the Commonwealth of Nations, but his indecision on whether to accept Bomarc nuclear missiles from the United States led to his government's downfall. Diefenbaker is also remembered for his role in the 1959 cancellation of the Avro Arrow project.

In the 1962 federal election, the Progressive Conservatives narrowly won a minority government before losing power altogether in 1963. Diefenbaker stayed on as party leader, becoming Opposition leader, but his second loss at the polls prompted opponents within the party to force him to a leadership convention in 1967. Diefenbaker stood for re-election as party leader at the last moment, but only attracted minimal support and withdrew. He remained in parliament until his death in 1979, two months after Joe Clark became the first Progressive Conservative prime minister since Diefenbaker. Diefenbaker ranks average among historians and the public.