Thomas Bowhill qualified as a member of the Royal College of Veterinary Surgeons (MRCVS) at the New Veterinary College, Edinburgh, in April 1886. His publications during the next few years indicate that he worked in California, United States, for some time: "Anthrax and Southern Fever among California Cattle" (Annual Report of the Bureau of Animal Industry, United States Department of Agriculture, 1889); "The cattle industry of California" (Ibid, 1889, as co-author of A.S. Mercer); and The Alvarado artesian water of the Oakland Water Company compared with the surface waters of Lake Temescal and Lake Chabot of the Contra Costa Water Company. A bacteriological analysis... (Oakland, 1895?, 45p). He probably returned to Europe towards the end of the decade, where he published a book, Manual of bacteriological technique and special bacteriology (Edinburgh, 1899, 284p) and a paper, "Zur bakteriologischen Technik. Zur Kultur der Hefen auf Gypsflaechen. Eine neue Platinnadel" (Centralblatt fuer Bakteriologie (Abteilung 2), 1899).
During the Anglo-Boer War (1899-1902 Bowhill appears to have come to the Cape Colony as a civil veterinary surgeon attached to the Army Veterinary Department. After the war, in July 1902, he was appointed by the government of the Cape Colony as an assistant veterinary surgeon under D. Hutcheon*. In July 1905, following the retirement of Dr A. Edington*, he assumed control of the former Colonial Bacteriological Institute in Grahamstown, which had just been renamed the Veterinary Laboratory. However, he left the service of the government in 1906, being succeeded in his post by W. Robertson*.
By 1905 Bowhill was a Fellow of the Royal College of Veterinary Surgeons, as well as a Fellow of the Royal Photographic Society. During 1905 he did some bacteriological research at Grahamstown on cases of "lamsiekte" (botulism) in the Eastern Cape, which was written up in an article on "Stock diseases of the eastern coastal districts" in the Agricultural Journal of the Cape of Good Hope (1906, Vol. 6, pp. 550-567). His other publications around this time included papers on 'Equine Piroplasmosis or Biliary Fever' (1905) and 'Note on Haematozoa observed in a bat' (1906), both in the Journal of Hygiene.
By 1921 Bowhill was a veterinary officer in Kampala, Uganda. At some time he was honoured as a Member of the Order of the British Empire (MBE).