Sir William McMahon was an Australian politician who served Prime Minister of Australia from 1971-1972. He was first elected to parliament in 1949, and held the Sydney seat of Lowe until his retirement in 1982. During his long career McMahon served as Minister for Primary Industry (1956–58) and Minister for Labour and National Service (1958–66) in the government of Robert Menzies. he was later appointed Treasurer (1966–69) in the governments of Harold Holt, John McEwen and John Gorton, and as Minister for External Affairs (1969–71) in the Gorton government.