"JB" Quinlan qualified as a veterinarian (MRCVS, Dublin) in 1912 and was awarded the Fitzwygram 1st Prize as the top veterinary student in the British Isles. He then came to South Africa as lecturer in veterinary science at the Potchefstroom College of Agriculture. During World War I (1914-1918) he served as a captain in the South African Veterinary Corps. In 1920 he was stationed at the Allerton Veterinary Laboratory in Natal, until his appointment in 1922 as the first professor of surgery, gynaecology and obstetrics at the newly established Faculty of Veterinary Science of the Transvaal University College at Onderstepoort, Pretoria. He served in this position until his retirement in 1947. In 1922 he was awarded the degree Dr.Med.Vet. (Hanover), followed by an FRCVS in 1928. The next year he obtained the degree DVSc (University of South Africa) for his thesis Researches into sterility of cattle in South Africa.
Quin publish widely on subjects related to surgery and reproduction in domestic animals. After his retirement he practiced in Cape Town, Mooi River and Durban until his death. He was widely regarded as the greatest equine veterinary surgeon of his time.