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
Secretary of the Department of the Prime Minister and Cabinet (Australia) the list of Secretaries, since the first appointment was made on 1 January 1912. Within days of John Gorton becoming Prime Minister, the functions of the Prime Minister's Department was split and a Department of the Cabinet Office was established. On taking office as Prime Minister in 1971, William McMahon reversed Gorton's changes and restored earlier changes via the creation of the Department of the Prime Minister and Cabinet. A lesser role of Secretary to the Department of the Vice-President of the Executive Council was established for a short time; abolished in the early days of the Whitlam government. Upon