Feetham was appointed deputy town clerk of Johannesburg in October 1902; he served under the town clerk, Lionel Curtis, who was a friend from his New College days. In April 1903 Feetham became the town clerk when Curtis was made Assistant Colonial Secretary. Two years later, in April 1905, Feetham resigned from the Town Council and was appointed to the South African Bar; he acted as legal adviser to the High Commissioner of South Africa from 1907-1910, and again from 1912-1923. In 1907 Feetham began his political career as a member of the Transvaal Legislative Council (1907-1910). In 1915 he was elected to the Union House Assembly as a Unionist for the Parktown constituency in Johannesburg; he later became a member of the South African Party. During World War I, Feetham gained a commission in the South African Cape Corps and served in East Africa and briefly in Egypt (1916-1918). Feetham resigned from Parliament in 1923 to take silk, and was appointed to the bench of the Transvaal Division of the Supreme Court. In 1930 he was appointed Judge President of the Natal Provincial Division, and in 1939 became Judge of Appeal in Bloemfontein. In 1938, Feetham was elected vice-chancellor of the University of the Witwatersrand, Johannesburg, and became its chancellor in 1949. He was also appointed chairman of various commissions both in South Africa and abroad including the Southborough Committee on Constitutional Reform in India (1918-1919), the Irish Boundary Commission (1924-1925), the Kenya Local Government Commission (1926), the Shanghai Municipal Council Commission (1930-1931), the Transvaal Asiatic Land Tenure Commission (1932-1935), and the Witwatersrand Land Titles Commission (1946-1949).