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
Acting prime minister Minister on 16 separate occasions. The term "acting Prime Minister" is sometimes also applied to someone who is temporarily appointed Prime Minister following a death in office (more commonly called a "caretaker Prime Minister" or an "interim Prime Minister"). Examples include Frank Forde (seven days following John Curtin's death), Earle Page (19 days following Joseph Lyons' death), and John McEwen (22 days following Harold Holt's disappearance). Unlike those who merely acted in the absence of a Prime Minister, Forde, Lyons, Page and McEwen were officially commissioned by the Governor General and took the oath of office; they are considered Prime