Rowntree has been a keen activist and supporter of the Labour Party since becoming a member in 2002, and has been chairman of London's West End branch. In April 2007 he unsuccessfully contested the safe Conservative seat of Marylebone High Street on Westminster City Council. In July 2008, he fought the Labour-held seat of Church Street, a Labour stronghold since its creation in the 1960s, but a swing from Labour to the Conservatives of 14.1% meant that he was again unsuccessful, as the Conservatives gained the seat.