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 New Zealand and Cabinet. The separate Private Office of the Prime Minister provides advice and support on political party matters. The style of "The Right Honourable" (abbreviated to "The Rt Hon") is always granted to the prime minister. Former prime ministers retain this style for the remainder of their lives. The written form of address for the head of government should use his or her full parliamentary title as applicable: "The Right Honourable [name], [post-nominal letters], Prime Minister of New Zealand". Should a serving or former prime minister die, he or she is accorded a state funeral (subject to the approval of