Robert William Ainsworth (born 19 June 1952) is a British Labour politician, who has been the Member of Parliament for Coventry North East since 1992, and is the current Secretary of State for Defence, replacing John Hutton on 5 June 2009.

Ainsworth was born in Coventry and attended the local Foxford Comprehensive School. He first became active in politics as a trade unionist at the Jaguar Cars plant in Coventry where he worked and served in many union capacities, including as Branch President (in what was later to become part of the Manufacturing, Science and Finance union). At this time he attended "a couple" of International Marxist Group meetings before deciding not to pursue an interest in the group. In 1984, he was elected to Coventry City Council, became Chair of the Finance Committee, and was deputy leader of the ruling Labour group. He was also Constituency Labour Party Chairman.

Ainsworth became Labour candidate for Coventry North East in the run-up to the 1992 general election after the sitting MP, John Hughes, was de-selected by the Constituency Labour Party. Ainsworth was successfully elected with a 11,676 majority, and stepped down from the city council the following year. At the 1997 general election his majority rose sharply to 22,569, falling back to 15,751 at the 2001 election, and 14,222 at the 2005 election.