Keen's first role in Parliament came in 1999 when she was appointed as Parliamentary Private Secretary to Frank Dobson, Secretary of State for Health, though this appointment lasted less than a month. She then moved to the Treasury, later becoming Parliamentary Private Secretary to the then Chancellor of the Exchequer, Gordon Brown. In 2000 Keen became well known for campaigning on gay rights, her interest in the issue sparked when she was reunited with her gay son who she had given up for adoption. In the same year she also successfully ran a campaign to elect Michael Martin as Speaker to the House of Commons.