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 Ben Chifley lived the least of all former prime ministers, as he died one year and six months after his term as prime minister. All other deceased former prime ministers have lived at least another 10 years, with the longest surviving former prime minister being Gough Whitlam, who lived 38 years and 11 months after office, surpassing Stanley Bruce's previous record of 37 years and 10 months. The youngest person to become prime minister was Chris Watson37, who was also 37 when he ceased being prime minister. The oldest person to become prime minister was John McEwen67 as an interim