William M. Power qualified as a veterinarian (MRCVS) at the Royal Veterinary College, London, in 1896. After practicing for a few years in Dublin he joined the Natal Civil Veterinary Department in June 1899. As a lieutenant in the Volunteer Veterinary Corps he served through the siege of Ladysmith during the Anglo-Boer War (1899-1902) and also during the Bambatha (Zulu) rebellion of 1906. He was appointed as a District Veterinary Surgeon in June 1901 and after a spell at Ixopo was transferred to Pietermaritzburg in 1905 to act as Principle Veterinary Officer of Natal in the absence of S.B. Woollatt*. In November 1907, on the latter's resignation, he was promoted to this post which he filled until the administration was reorganised following the formation of the Union of South Africa in 1910, when he became Senior Veterinary Surgeon for Natal until his retirement in 1928. During this period he published a number of short papers on animal diseases.
Power became a member of the Royal Agricultural Society in Pietermaritzburg in 1910 and served as its President from 1929 to 1934. After retiring he started a private practice in Pietermaritzburg and took an active interest in local affairs, especially the game reserves of Natal. He was President of the Royal Agricultural Society of Natal from 1929-1935 and a member of the Natal Provincial Council from 1931 to 1946 (from 1933 to 1946 as a member of the executive council). In 1935 he was appointed Chairman of a commission to investigate the game reserves of Zululand and from 1939 to 1947 served as chairman of the Zululand Game Reserves and Parks Board. In 1947 he became the first chairman of the Natal Parks Board and served this body until 1950, shortly before his death. He also had an interest in historical matters and was a member of both the Historical Monuments Commission and the 1820 Settlers Memorial Association, serving the latter as chairman. His contribution to wildlife conservation is commemorated in a memorial gate to the Hluhluwe Game reserve.