She was the Member of Parliament (MP) for Mid Dorset and North Poole from the 2001 general election to 2015. At the time she left office, Brooke was the longest serving female MP in the history of the Liberal Democrats.
Brooke was educated at Romford County Technical School in Romford and the London School of Economics, graduating with a BSc degree in Economics. She qualified as a teacher at Hughes Hall, Cambridge. She was a tutor with the Open University for 19 years from 1971 and was a school teacher from 1974, including at Aylesbury, and then Head of Economics at the independent Talbot Heath School for Girls in Bournemouth, which she left in 1994.
Annette Brooke was elected as a councillor on Poole Borough Council in 1986; she was the council's deputy leader 1995–7 and 1998–2000, and the Liberal Democrat Group Leader 2000–1. She was the Mayor of Poole in 1998. She contested the Conservative-held seat of Mid Dorset and Poole North at the 2001 General Election.
At the previous election the Conservative Christopher Fraser won the seat by 681 votes. In 2001 Annette Brooke was elected by 384 votes and held the seat until 2015 where it was regained by the Conservatives. She made her maiden speech on 21 June 2001.
In Parliament she was made both a Liberal Democrat Whip and a Spokeswoman on Home Affairs by Charles Kennedy in 2001. In 2004 she became a spokeswoman on Children. Following the 2005 General Election (at which Annette Brooke held her seat with a much increased majority of 5,482), she became a spokeswoman on Education and Skills, and carried on in a similar position as spokeswoman on Children, Schools and Families.