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
Deputy Prime Minister of Australia and Julia Gillard. In both cases, they succeeded incumbent Prime Ministers who lost the support of their party caucus mid-term and their election as party leader preceded their predecessor's resignations and their subsequent appointments as Prime Minister. Frank Forde, who had been deputy Labor leader when John Curtin died, was interim Prime Minister between 6 and 13 July 1945, when a leadership ballot took place that elected Ben Chifley as Curtin's successor. In November 2007, when the Australian Labor Party won government, Julia Gillard became Australia's first female, and first foreign-born, Deputy Prime Minister. In 2017, the position became vacant