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 Bahrain's prime minister, Sheikh Khalifah bin Sulman Al Khalifah has been in the post since 1970, making him the longest serving non-elected prime minister. The post of prime minister may be encountered both in constitutional monarchies (such as Belgium, Denmark, Japan, Luxembourg, the Netherlands, Norway, Malaysia, Morocco, Spain, Sweden, Thailand, Canada, Australia, New Zealand, and the United Kingdom), and in parliamentary republics in which the head of state is an elected official (such as Finland, the Czech Republic, France, Greece, Hungary, India, Indonesia (1945-1959), Ireland, Pakistan, Portugal, Montenegro, Croatia, Bulgaria, Romania, Serbia and Turkey (1923-2018)). See also "First Minister", "Premier",