John Thorburn graduated as Bachelor of Veterinary Science (BVSc) at the Veterinary Faculty of Pretoria University College at Onderstepoort in 1928. From January 1929 he served as government veterinary officer in the Division of Veterinary Services and was stationed in Pietermaritzburg (1929), at the Onderstepoort Research Institute, in the Northern Cape, Zululand, Peddie (in the Transkei), Grahamstown and, from March 1942, East London, until 1945. During this period he published two scientific papers. One of these dealt with the toxic effect on ruminants of Cestrum laevigatum (Fam. Solanaceae), or inkberry plant, and was published in the Onderstepoort Journal of Veterinary Science in 1934.
Thorburn became a member of the South African Veterinary Medical Association in 1929. Upon resigning his post in 1945 he joined Cooper and Nephews as technical advisor until his retirement in September 1968.