David Albert Lloyd Johnston is an Australian politician who was a Liberal Party member of the Australian Senate from 2002 to 2016, representing the state of Western Australia. Johnston was the Minister for Defence from 18 September 2013 to 23 December 2014, when he was replaced by Kevin Andrews.

The minister for Defence, also known as the Defence minister, is the minister of state of the Commonwealth of Australia charged with overseeing the organisation, implementation, and formulation of strategic policy in defence and military matters as the head of the Department of Defence. The Defence minister directs the government’s approach to the Australian Defence Organisation and the Australian Defence Force. The current Defence minister is Richard Marles, who is concurrently serving as deputy prime minister of Australia, he was selected by Prime Minister Anthony Albanese in May 2022 following the 2022 Australian federal election.