J.H.L. Cloete received the Reyersback Memorial Prize for the best matriculation science pass in the Union of South Africa in 1927. He obtained his BVSc degree at the Veterinary Faculty, Onderstepoort, in 1932. He then joined the Division of Veterinary Services and served as state veterinarian at Rustenburg, Ermelo and Onderstepoort, where he lectured in comparative anatomy and embryology. In 1939 the University of South Africa awarded him the DVSc degree for a thesis on "Prenatal growth of the Merino Sheep". A paper based on his thesis, "The estimation of the age of Merino foetuses" earned him the Junior Gold Medal of the British Association for the Advancement of Science. Early in 1940 he resigned his post to take up a part-time appointment as veterinary officer to the municipalities of Springs and Brakpan and to conduct private practice at Springs. But within a few months he moved to Pretoria as acting municipal veterinary officer for the duration of World War II. He had just assumed the editorship of the Journal of the South African Veterinary Medical Association, and been elected to the council of the Association, when he died prematurely on 7 November 1940 after a short illness.
Cloete was married to Mary Edith Richardson. He had no children, but his wife had two children from her previous marriage.