Ian Sinclair, Australian farmer and politician, 42nd Australian Minister for Defence
Ian McCahon Sinclair (born 10 June 1929) is a former Australian politician who served as leader of the National Party from 1984 to 1989. He was a government minister under six prime ministers, and later Speaker of the House of Representatives from March to November 1998.

Sinclair was born in Sydney and studied law at the University of Sydney. He later bought a farming property near Tamworth. Sinclair was elected to parliament in 1963, and added to the ministry in 1965 as part of the Menzies Government. Over the following six years, he held various portfolios under four other prime ministers. Sinclair was elected deputy leader of his party in 1971, under Anthony. He was a senior member of the Fraser Government, spending periods as Minister for Primary Industry (1975–1979), Minister for Communications (1980–1982), and Minister for Defence (1982–1983). In 1984, Sinclair replaced Anthony as leader of the Nationals. He led the party to two federal elections, in 1984 and 1987, but was replaced by Charles Blunt in 1989. Sinclair was father of the parliament from 1990 until his retirement at the 1998 election. He spent his last months in parliament as Speaker of the House of Representatives, following the sudden resignation of Bob Halverson; he is the only member of his party to have held the position. He also served as co-chair of the 1998 constitutional convention, alongside Barry Jones.

Along with Peter Nixon, Sinclair is one of two Country/Nationals MPs elected in the 1960s still alive, and he is the last surviving minister who served in the Menzies Government and the First Holt Ministry, and who is entitled to the Right Honourable prefix.