Kenworthy first tried to enter Parliament at the 1918 general election contesting Rotherham as a Liberal but finished in third place. He was soon given another chance though when he was selected to contest Central Hull at a by-election in 1919. Anti-Coalition government sentiment was riding high and he was duly elected Member of Parliament for the Liberals. Kenworthy was one of the more energetic supporters of H H Asquith in Parliament and never lost his hostility to Lloyd George. During the 1924-29 parliament which was dominated by a Conservative majority, he worked closely with a group of radical Liberal MPs that included: William Wedgwood Benn, Percy Harris, Frank Briant and Horace Crawfurd to provide opposition to the government.