As Lord Dunglass, the courtesy title he held until he succeeded in 1951 to the earldom of Home, he sat in the House of Commons as a Unionist (1931–45, 1950–51). He served as parliamentary private secretary to Prime Minister Neville Chamberlain (1937–39), undersecretary of state for foreign affairs in Winston Churchill's “caretaker” government (May–July 1945), minister of state for Scotland (1951–55), secretary of state for Commonwealth relations (1955–60), deputy leader (1956–57) and leader (1957–60) of the House of Lords, and lord president of the council (1957–60) before his first term as foreign secretary. In October 1963 he disclaimed his peerages for life, took the name Sir Alec Douglas-Home, and succeeded Harold Macmillan as prime minister during a Conservative Party crisis, the most spectacular feature of which was an adultery scandal involving John Dennis Profumo, secretary of state for war from 1960 to 1963.

Admittedly having slight knowledge of economics, Sir Alec as prime minister was unable to improve the deteriorating British balance-of-payments situation. He antagonized numerous Conservatives by inducing the House of Commons to pass legislation against price-fixing. Both as foreign secretary and as prime minister, he gained U.S. approval for his firm anti-Communism. As chairman of the Commonwealth Prime Ministers' Conference (July 1964), he achieved some compromise between extremist views on racial problems. Throughout his ministry he was faced with the prospect of a forthcoming general election, which took place on Oct. 15, 1964, and brought a Conservative defeat. He was succeeded (July 1965) as party leader by the future prime minister Edward Heath. In December 1974 he was created a life peer, Baron Home of the Hirsel of Coldstream. In 1976 he published his autobiography, The Way the Wind Blows. He also published Border Reflections: Chiefly on the Arts of Shooting and Fishing (1979) and Letters to a Grandson (1983).