Lewis started his political career in 1910 when he moved to London to serve as private secretary to Freddie Guest, Liberal MP for East Dorset. After military service in World War One, Lewis secured the nomination for Pontypridd as a Coalition Liberal and was elected at the 1918 general election, fighting off both Labour and Conservative opponents. In parliament Lewis campaigned for Welsh home rule and the rights of Nonconformists. With his former employer Freddie Guest in the government as Chief Whip, Lewis was appointed Parliamentary Private Secretary and when Guest became Secretary of State for Air, Lewis moved with him. In 1922 Lewis was appointed a Junior Lord of the Treasury but lost the ensuing by-election which was required on appointment to government office. Four months later Lewis was back in parliament as MP for the University of Wales but sadly in July 1923 Lewis died aged only 41.