(1866-1937) a British prime minister. He was leader of the Labour Party (1911-14 and 1922-31) and the first Labour prime minister (1924 and 1929-31). His second government failed to deal with economic difficulties, and was replaced by a coalition government (= one supported by all parties). MacDonald continued as prime minister (1931-5), but left the Labour Party, an act which made him unpopular with Labour supporters. In 1935 he resigned and was replaced by Stanley Baldwin.