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 Australia his previous status as the second-ranking member of the government, as per the Coalition agreement. He had unofficially been Deputy Prime Minister since becoming Country Party leader in 1958, and since 1966 had exercised an effective veto over government policy by virtue of being the longest-serving member of the government; he had been a member of the Coalition frontbench without interruption since 1937. To acknowledge McEwen's long service and his status as the second-ranking member of the government, Gorton formally created the post of Deputy Prime Minister, with McEwen as the first holder of the post. Governor-General Lord Casey also