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
Australian home front during World War II to the declaration, and Parliament passed the "National Security Act 1939". A War Cabinet was formed after the declaration of war, initially composed of Prime Minister Menzies and five senior ministers (RG Casey, GA Street, Senator McLeay, HS Gullet and World War I Prime Minister Billy Hughes). When Page still refused to join a government under Menzies, he was replaced by Archie Cameron as leader of the Country Party on 13 September 1939, allowing the conservative parties to re-form a Coalition by March 1940. The recruitment of a volunteer military force for service at home and abroad was announced, the