James L. Webb, son of James Webb, FRCVS, qualified as a veterinarian (MRCVS, London) in March 1896. He was one of four veterinarians appointed that same year by the colonial authorities in Natal, on the recommendation of the Stock Commission, to combat rinderpest. His first station was at Ixopo. By 1899 he was district veterinary surgeon at Bulwer. During the Anglo-Boer War (1899-1902) he served as a civil veterinarian in the Army Veterinary Department and later with the Natal Voluntary Veterinary Corps. In 1900 he published a short article on Distomiasis, or liver fluke disease, in the Natal Agricultural Journal (Vol. 3, pp. 417-418). At the end of his five year contract he returned to England and was awarded the FRCVS in 1902 for a thesis entitled "The treatment of Rinderpest".
Webb subsequently returned to Natal and on 1 January 1903 was appointed district veterinary surgeon. He served in this capacity at Howick (1904, 1908), Mooi River (1905), Ixopo (1906), Ladysmith (1907), and Port Shepstone (1910). After the formation of the Union of South Africa in 1910 he continued to serve as a district veterinary surgeon in the province of Natal until he retired in September 1928. Thereafter he settled in Ixopo and later Pietermaritzburg. From 1904 he published further articles on livestock diseases in the Natal Agricultural Journal, dealing with Gall sickness (1904, Vol. 7, p. 82), vegetable poisoning among stock (Ibid, p. 1101), Diseases of the stomach in ruminants (1905, Vol. 8, pp. 1183-1190 and 1906, Vol. 9, pp. 1-7), and Tetanus (1907, Vol. 10, pp. 95-99). Later an article by him appeared in the Agricultural Journal of the Union of South Africa, dealing with "Actinomycosis Bovis (Lumpy Jaw) in Natal" (1911, Vol. 2). He became a member of the South African Veterinary Medical Association in 1924.
On 20 September 1898 Webb married Alice Agatha Calvert Hardwicke, but they were divorced around 1908. Later he was married to Agnes Brown, who died in 1948.