Sir Sidney Horatio Marshall (17 July 1882-28 March 1973) was a Conservative Party politician active in the Sutton and Cheam area of Surrey, which became part of Greater London in 1965. Born in Mitcham, Marshall became an industrialist and was elected to Surrey County Council in 1931 and to Sutton and Cheam Urban District Council in the following year. He became a county alderman in 1941 and was chairman of Surrey County Council from 1947-50. He was charter mayor when Sutton and Cheam was incorporated as a municipal borough in 1934, and served as mayor again in 1936-37. He remained an alderman, and was created an honorary freeman of the borough in 1948.