St. Laurent, Louis Stephen (1882–1973), the 12th prime minister of Canada and the second French-Canadian to hold the office. Under his leadership, 1948–57, the unity of French-and English-speaking Canada was strengthened and Canada increased its role in world affairs. He expanded the nation's social services, persuaded the United States to help build the St. Lawrence Seaway, and was one of the first to propose a North Atlantic alliance.
St. Laurent was born in Compton, Quebec, the son of a French-Canadian father and a mother of Irish ancestry. After receiving a law degree from Laval University in 1905, he became a leading corporation lawyer. A member of the Liberal party, St. Laurent entered active politics in 1941 at the request of Prime Minister Mackenzie King. He was appointed minister of justice and attorney general for the duration of World War II. In 1942 he was elected to the House of Commons. He served as deputy chairman of the Canadian delegation to the United Nations organizing conference in 1945 and headed Canada's UN delegation, 1946–47. In 1946 he became secretary of state for external affairs.
In 1948 St. Laurent succeeded King as leader of the Liberal party and as prime minister. After election victories in 1949 and 1953, the Liberals lost control of the government in 1957. St. Laurent then retired from active politics.