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 Prime Minister of Australia The Prime Minister of Australia is the head of government of Australia. The individual who holds the office is the most senior Minister of State, the leader of the Cabinet. The Prime Minister also has the responsibility of administering the Department of the Prime Minister and Cabinet, and is the chair of the National Security Committee and the Council of Australian Governments. The office of Prime Minister is not mentioned in the Constitution of Australia but exists through Westminster political convention. The individual who holds the office is commissioned by the Governor-General of Australia and at