Prime Minister of Australia prime minister, otherwise William McMahon63. Robert Menzies was the oldest person to ever be prime minister, leaving office at 71 years old. The longest-serving Prime Minister was Sir Robert Menzies, who served in office twice: from 26 April 1939 to 28 August 1941, and again from 19 December 1949 to 26 January 1966. In total Robert Menzies spent 18 years, 5 months and 12 days in office. He served under the United Australia Party and the Liberal Party respectively. The shortest-serving Prime Minister was Frank Forde, who was appointed to the position on 6 July 1945 after the death of
Menzies Government (1949–66) narrowly returned against Labor's Arthur Calwell in the December 1961 election, in the midst of a credit squeeze. Menzies stood for office for the last time in the November 1963 election, again defeating Calwell, with the Coalition winning back its losses in the House of Representatives. Menzies went on to resign from parliament on 26 January 1966. Menzies' 1949 Cabinet had the leader of the Country Party, Arthur Fadden, as the Treasurer and Deputy Prime Minister and included Dame Enid Lyons as the first woman to serve in an Australian Cabinet. After winning office in 1949, Menzies fulfilled his promises