Brendan John Nelson (born 19 August 1958) is an Australian business leader and former politician. He served as the federal Leader of the Opposition from 2007 to 2008, going on to serve as Australia's senior diplomat to the European Union and NATO. He now has a global leadership role with Boeing, an aerospace company.

A medical doctor by profession, he came to public prominence as the Federal President of the Australian Medical Association (1993–95), and served as a Minister in the third and fourth terms of the Howard Government, serving as Minister for Education, Science and Training (2001–06) and Minister for Defence (2006–2007).

Nelson was a member of the House of Representatives from 1996 to 2009, as the Liberal member for the Division of Bradfield in northern Sydney.

Following the 2007 federal election, at which the Howard Government was defeated, Nelson was elected leader of the Liberal Party in a contest against former Minister for Environment and Water Resources Malcolm Turnbull, and became the Leader of the Opposition on 3 December 2007. On 16 September 2008, in a second contest following a spill motion, Nelson lost the leadership of the Opposition and the Liberal Party to Turnbull.

Nelson retired from politics in 2009, and was Ambassador to Belgium, Luxembourg, the European Union and NATO from 2009 to 2012. He was then Director of the Australian War Memorial from 2012 to 2019, subsequently serving as its chair until the end of 2022.

In February 2020, Nelson was made the President of Boeing Australia, New Zealand, and South Pacific. In September 2022, it was announced he would move to London to become President of Boeing International.