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
Prime Minister of Australia the Governor-General's pleasure subject to the Constitution of Australia and constitutional conventions. Scott Morrison has held the office of Prime Minister since 24 August 2018. He received his commission after replacing Malcolm Turnbull as the leader of the Liberal Party, the largest party in the Coalition government, following the Liberal Party leadership spill earlier the same day. The Prime Minister of Australia is appointed by the Governor-General of Australia under Section 64 of the Australian Constitution, which empowers the Governor-General, as the official representative of the Crown, to appoint government ministers of state on the advice of the Prime Minister