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 Portugal was sworn in on 24 September 1834, as "Presidente do Conselho de Ministros" (President of the Council of Ministers). In 1911, the official title of the prime minister became "Presidente do Ministério" (President of the Ministry). In 1933, it became again "Presidente do Conselho de Ministros". The present title "Primeiro-Ministro" (Prime Minister), attributed to the head of the Government of Portugal, was officially established by the Constitution of 1976 after the revolution of 25 April 1974 The incumbent Prime Minister of Portugal is António Costa, who took office on 26 November 2015 as the 13th Prime Minister of the Third