Fiona Margaret Mactaggart (born 12 September 1953, Glasgow) is a politician in the United Kingdom. She is Labour member of Parliament for the Slough parliamentary constituency. Until the May 5, 2006 Cabinet reshuffle, she served at the Home Office as Parliamentary Under-Secretary of State with responsibility for Criminal Justice and Offender Management.

She was first elected to Parliament in 1997. She was a councillor and Leader of the Labour Group on Wandsworth Council from 1988 to 1990. She has been a primary school teacher and Chair of Liberty.

Her father, the late Sir Ian Mactaggart Bt, was a multimillionaire Glasgow property developer, Conservative candidate and Eurosceptic. Her mother's father, Sir Herbert Williams Bt, was a Conservative Member of Parliament for 27 years. Her great-grandfather however was Sir John Mactaggart, the first treasurer of the first ever branch of Keir Hardie's Labour Party.