Phillipus Lodewicus ("Gin") Le Roux was the eldest son of Phillipus Lodewicus Le Roux, a farmer near Worcester. His early education was at Rawsonville Public School, Worcester, and at the South African College School in Cape Town. He then went to Edinburgh and in 1923 obtained a BSc degree from the University of Edinburgh and his MRCVS at the Royal (Dick) Veterinary College. He devoted a year to post-graduate study in helminthology in the Department of Parasitology, University of Edinburgh, before returning to South Africa to join the Division of Veterinary Services. He was first posted to the Allerton Laboratory in Natal, then to the Ermelo experimental farm, and finally to the Helminthology Section at the Onderstepoort Veterinary Research Institute as a veterinary research officer. He also lectured in veterinary hygiene, animal management and veterinary helminthology in the Faculty of Veterinary Science of the University of Pretoria. From 1924 onwards he published about 50 papers on helminth parasites of domestic and wild animals and came to be recognised as an authority on the Schistosome group of parasitic worms and on agnatic snails, which act as intermediaries of flukes of veterinary and medical importance.
Le Roux left South Africa in 1931 for an appointment as veterinary research officer (later senior veterinary research officer) in the government service of Northen Rhodesia (now Zambia). Here he worked on rinderpest, contagious bovine pleuroneumonia, the acyclical transmission of trypanosomiasis, and described "pseudo-urticaria in cattle" - the first reference to a disease later encountered in South Africa and now known as Lumpy Skin Disease. A DSc degree was conferred on him by the University of Edinburgh in 1936.
In 1946 ill health forced him to retire, whereupon he joined the staff of the London School of Hygiene and Tropical Medicine as senior lecturer in helminthology. He became reader in medical parasitology at the same institution in 1957, until his death in 1962. For several years he was associated with the Food and Agricultural Organisation of the United Nations, training persons from all over the world in parasitology and visiting several African countries. In addition to his work in parasitology he published more than 30 papers on protozoology, entomology, and virus diseases.
Le Roux had a good memory, an enquiring mind, keen powers of observation and an enormous capacity for work. A restless, impatient and quick-tempered person with a complex personality, completely unimpressed by authority, but a brilliant parasitologist who contributed significantly to our knowledge of African helminths.