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 Thailand sixteen out of twenty-nine, including the incumbent General Prayut Chan-o-cha. Military dominance began with the country's second Prime Minister, Phot Phahonyothin, who ousted his civilian predecessor in a coup in 1933. The longest serving Prime Minister was Field Marshal Plaek Pibulsonggram at 14 years, 11 months and 18 days. The shortest was Tawee Boonyaket at just 18 days. Nine were removed by coups d'état, three were disqualified by court order, and eleven resigned from office. The youngest ever to occupy office was M.R. Seni Pramoj at 40 years old. Thailand received its first female prime minister, Yingluck Shinawatra, in 2011.