She was Conservative Party Member of Parliament (MP) for Hornchurch and Upminster until 2017, and was first elected in 2001 to the earlier seat of Upminster, defeating Labour's Keith Darvill who had taken the seat from the Conservatives in 1997.
She was re-elected with an increased majorities in 2005 and 2010.
On 19 April 2017, Watkinson announced that she would not be standing for re-election in the 2017 general election.