Pearson entered politics in 1948, as Minister of External Affairs in the Liberal government of Louis St. Laurent. He became leader of the Liberal Party in 1958. He lost two elections as leader, until winning a third to become Prime Minister in 1963. His government brought in social programs and new standards for workers. Pearson signed the Canada-United States Automotive Agreement, also called the Auto Pact. He retired in 1968. The next Prime Minister was Pierre Trudeau.