In 1906 he was elected Conservative Member of Parliament for the Kingston Division of Surrey, was appointed Vice-Lieutenant of Surrey in 1907, and a member of the Royal Commission on Land Purchase in 1908. Having served as standing Counsel to the University of Oxford for two years as well as Attorney General to the Prince of Wales, in 1915 Cave was appointed Solicitor General and knighted. The following year, he was made Home Secretary in Lloyd George's coalition government, a post he held for three years. As Home Secretary, he introduced the Representation of the People Act 1918 and he was very prominent in the debates in the House of Commons on the police strike of August 1918.