Sir William McMahon was an Australian politician who became the 20th Prime Minister of Australia; he served as Prime Minister from March 1971 to December 1972. Being a member of parliament for over 21 years, he became the longest serving minister in the history of Australian Government. He began his career as a lawyer and went on to join the Australian army during World War II. His political career began when he was elected to the House of Representatives in 1949. With his hard work and enthusiasm, he rose in prominence and held several important portfolios in the Robert Menzies government. As Minister for Labour, he passed The National Service Act of 1964. Later, when Harold Holt became Prime Minister, he became the deputy leader of the Liberal Party and was appointed Treasurer. After Holt’s death, he wanted to contest for the Liberal Party leadership but he failed to win the confidence of John McEwen, leader of the Country Party. He continued as a Treasurer in the new John Gorton’s government but was eventually demoted to Minister of External Affairs, following another failed attempt for leadership. In 1971, Gorton resigned and he won a vote against Billy Snedden to finally become Prime Minister 3. In 1972, he suffered defeat in the hands of the Labor Party and decided to give up the Liberal Party leadership. Thereafter, he continued in Parliament as a backbencher for another decade. He was knighted in 1977.