Malthouse served on the Westminster City Council from 1998 to 2006 and was Deputy Council Leader from 2004 to 2006. He served as a Conservative member of the London Assembly for West Central from 2008 to 2016. He represented the City of Westminster, the London Borough of Hammersmith and Fulham and the Royal Borough of Kensington and Chelsea. He served under Mayor of London Boris Johnson as Deputy Mayor for Policing from 2008 to 2012 and Deputy Mayor for Business and Enterprise from 2012 to 2015.