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 the Philippines the title of "Prime Minister", thus re-creating the office after 1899. Marcos, who concurrently as President, continued to wield the powers vested in the President by the 1935 Constitution. The Amendment also created the unicameral legislature known as the Interim Batasang Pambansa (Interim National Assembly or IBP), as well as a provision such that the President/Prime Minister will exercise legislative powers "until" martial law is lifted. On April 7, 1978, the first election for the Batasang Pambansa, was held since the abolition of the bicameral Congress under the 1973 Constitution. 150 out of 165 elected positions of the parliament were