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
Deputy Prime Minister of the United Kingdom his effective deputy. After the 2016 referendum on European Union membership, and David Cameron's subsequent resignation, his successor as Prime Minister, Theresa May, also chose not to appoint an individual to either position. Following the 2017 snap general election, May again did not appoint a Deputy Prime Minister but did appoint Damian Green as First Secretary of State. The Deputy Prime Minister's Office (DPMO) is a non-statutory office, only being formed when a deputy prime minister is appointed which consists of the staff members and advisers who assist the deputy prime minister in his or her role. The most recent