Joseph Philippe Pierre Yves Elliott Trudeau ( TROO-doh, troo-DOH, French: [pjɛʁ tʁydo]; October 18, 1919 – September 28, 2000) was a Canadian lawyer and politician who served as the 15th prime minister of Canada from 1968 to 1979 and from 1980 to 1984. He also briefly served as the leader of the Opposition from 1979 to 1980.

Trudeau was born and raised in Montreal, Quebec and studied politics and law. In the 1950s, he rose to prominence as a labour activist in Quebec politics by opposing the conservative Union Nationale government. Trudeau was then an associate professor of law at the Université de Montréal. He was originally part of the social democratic New Democratic Party, though felt they could not achieve power, and instead joined the Liberal Party in 1965. That year, he was elected to the House of Commons, quickly being appointed as Prime Minister Lester B. Pearson's parliamentary secretary. In 1967, he was appointed as minister of justice and attorney general. As minister, Trudeau embraced social liberalism; his two most notable achievements were decriminalizing homosexual acts and legalizing abortion. Trudeau's outgoing personality and charismatic nature caused a media sensation, inspiring "Trudeaumania", and helped him to win the leadership of the Liberal Party in 1968, when he succeeded Pearson and became prime minister of Canada.

From the late 1960s until the mid-1980s, Trudeau's personality dominated the political scene to an extent never before seen in Canadian political life. After his appointment as prime minister, he won the 1968, 1972, and 1974 elections, before narrowly losing in 1979. He won a fourth election victory shortly afterwards, in 1980, and eventually retired from politics shortly before the 1984 election. Trudeau is the most recent prime minister to win four elections (having won three majority governments and one minority government) and to serve two non-consecutive terms. His tenure of 15 years and 164 days makes him Canada's third-longest-serving prime minister, behind John A. Macdonald and William Lyon Mackenzie King.

Despite his personal motto, "Reason before passion", Trudeau's personality and policy decisions aroused polarizing reactions throughout Canada during his time in office. While critics accused him of arrogance, of economic mismanagement, and of unduly centralizing Canadian decision-making to the detriment of the culture of Quebec and the economy of the Prairies, admirers praised what they considered to be the force of his intellect and his political acumen that maintained national unity over the Quebec sovereignty movement. Trudeau suppressed the 1970 Quebec terrorist crisis by controversially invoking the War Measures Act, the third and last time in Canadian history that the act was brought into force. In addition, Quebec's proposal to negotiate a sovereignty-association agreement with the federal government was overwhelmingly rejected in the 1980 Quebec referendum. In a bid to move the Liberal Party towards economic nationalism, Trudeau's government oversaw the creation of Petro-Canada and launched the National Energy Program; the latter generated uproar in oil-rich Western Canada, leading to what many coined "Western alienation". In other domestic policy, Trudeau pioneered official bilingualism and multiculturalism, fostering a pan-Canadian identity. Trudeau's foreign policy included making Canada more independent; he patriated the Constitution and established the Canadian Charter of Rights and Freedoms, actions that achieved full Canadian sovereignty. He formed close ties with the Soviet Union, China, and Cuban leader Fidel Castro, putting him at odds with other capitalist Western nations.

In his retirement, Trudeau practised law at the Montreal law firm of Heenan Blaikie. He also campaigned against the later-unsuccessful Meech Lake and Charlottetown Accords, arguing the Accords recognizing Quebec as a "distinct society" would weaken federalism and strengthen Quebec nationalism. Trudeau died in 2000. He is ranked highly among scholars in rankings of Canadian prime ministers. His eldest son, Justin Trudeau, became the 23rd and current prime minister, following the 2015 Canadian federal election; Justin Trudeau is the first prime minister of Canada to be a descendant of a former prime minister.