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 as Prime Minister, until a colleague of higher rank is available again. Acting prime minister An acting Prime Minister is a cabinet member (often in Westminster system countries) who is serving in the role of Prime Minister, whilst the individual who normally holds the position is unable to do so. The role is often performed by the Deputy Prime Minister (where that position exists), or by another senior Minister. The office is commonly used when the Prime Minister is absent from the territory of that nation, when the Prime Minister is in ill health or, on maternity leave. An acting