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
Cabinet Secretary (Australian minister) Governments. The Cabinet Division is led by a First Assistant Secretary and includes the Cabinet Secretariat and the Strategic Coordination and National Security Branch. With the discontinuation of the ministerial Cabinet Secretary, the position is now an held by an Australian Public Service officer within Prime Minister's Office in support of the Cabinet Division of the Department of the Prime Minister and Cabinet. The following individuals have been appointed as Cabinet Secretary, with some serving concurrently: Cabinet Secretary (Australian minister) The Cabinet Secretary was a former title conferred on an Australian minister responsible for assisting the Prime Minister to manage