Isaac Pieter Marais, son of Isaac Pieter Marais and his wife Natalia Adamanta, born Maritz, obtained a BSc(Agric) in 1921 and a BVSc in 1925 from the Transvaal University College (later the University of Pretoria). He joined the Division of Veterinary Services of the Department of Agriculture in 1926 and remained in the service until 1938. During this period he was senior lecturer in the Department of Surgery and Gynaecology at Onderstepoort and published "Some experiments with vuilbek (Ecthyma Contagiosum)" (Journal of the South African Veterinary Association, 1928), "Diseases of the cow's udder" (East African Agricultural Journal, 1938), and some articles in Farming in South Africa. He alsocollaborated with J. Quinlan*, G. de Kock*, W. Neitz* and H.O. Monnig* on several other papers.
Marais was officer in charge of the Allerton Laboratory, near Pietermaritzburg, during 1930-1931. From 1935 to 1936 he studied in Leipzig, Germany, and wrote a thesis on Untersuchungen ueber den Sexualzyklus bei Merinoschafen (1936). In 1938 was appointed veterinary superintendent of the Pretoria municipal abattoir. In June that year he joined the SA Veterinary Corps with the rank of Major. He resigned from the Pretoria municipal service in 1953 and entered private practice in Alberton. He was married to Therese Nell Marais, born Erlich, but they were divorced in 1950. He was survived by his second wife, Sheila Pitt Marais, and three children.