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 Zimbabwe and held by Morgan Tsvangirai until the position was again abolished by the 2013 Constitution of Zimbabwe. Zimbabwe's prime ministerial office owes its origins to the country's predecessor states. The position began with George Mitchell who became Prime Minister of Southern Rhodesia in 1933. All subsequent predecessor-states continued with the post until Abel Muzorewa who became Prime Minister of Zimbabwe Rhodesia in 1979 under the Internal Settlement. The Lancaster House Agreement brought an independence constitution which made provision for a parliamentary system, with a President as head of state and a Prime Minister as head of government. The presidency was