Harriett was elected as the Member of Parliament for West Worcestershire in May 2010, where she has lived since 2006. She served as a member of the Work and Pensions Select Committee and from September 2012 to February 2014 she served as Parliamentary Private Secretary to the Minister for Employment in the Department of Work and Pensions. Harriett has represented the UK on the NATO Parliamentary Assembly, was elected Chair of the All-party Parliamentary Group for Russia and Vice-chair of the All-party Parliamentary Group for Occupational Pensions.
Harriett was appointed to become the Prime Minister’s Trade Envoy to Russia before joining the Government in February 2014 as Assistant Government Whip. In the July 2014 reshuffle she was promoted to Lord Commissioner.