Gilles De Kock qualified (MRCVS) in London in 1913 as one of the second group of two students sent to study veterinary science by the government of the Transvaal Colony in 1909. In February 1914 he was appointed to the staff of Sir Arnold Theiler* at the Onderstepoort Veterinary Laboratory and for a short period was stationed at the lamsiekte station "Armoedsvlakte", near Vryburg. In 1919 he returned to London to study medicine, but could not settle down and returned to South Africa in 1920 to take up a post as lecturer at the newly founded faculty of agriculture at the University of Stellenbosch, on the assumption that a Veterinary Faculty would be established there. When it was finally established (as part of the Transvaal University College) at Onderstepoort instead, he transferred to Pretoria and was appointed professor of anatomy. In 1923 he spent a year in Bern, Switzerland, and obtained the Dr.Med.Vet. degree. His thesis was titled Beitraege zur Kenntnis des Erregers, zur Haematologie und pathologischen Anatomie und Histologie der infectioesen Anaemie der Pferde, wie sie in Suedafrika beobachted wird (Pretoria, 1923), with Sir Arnold Theiler* as promotor.
Upon his return to South Africa in 1924 De Kock assumed the chair of pathology at Onderstepoort, the name of which was changed to comparative pathology in 1938. He held this position until his retirement in 1949. Since 1927 he simultaneously filled the position of sub-director of the laboratory and in 1948 succeeded P.J. Du Toit* as director of veterinary services and dean of the Veterinary Faculty. Dr De Kock was an academic par excellence who studied extensively in Europe and the USA. He obtained a DSc degree in zoology at the University of the Witwatersrand in 1928 for his thesis A study of the reticulo-endothelial system in sheep and published on a wide variety of veterinary problems. Several of his papers were published in the South African Journal of Science, for example, "Sarcosporidia" (1915), "The difference between anaplasma and Jolly bodies" (with J. Quinlan, 1926), "Fat necrosis in sheep" (1928) and "The spleen in ruminants and equines" (1929). His particular interest was haematology and the reticulo-endothelial system.
De Kock became a foundation member of the South African Biological Society in 1917, served as its president in 1932, and the next year was awarded the society's Senior Captain Scott Memorial Medal. In 1949 he served as president of the South African Association for the Advancement of Science and that same year received the association's South Africa Medal (Gold). He was also a fellow of the Royal Society of South Africa. After his retirement in 1949 he settled in Cape Town where he acted as an honorary research associate at the Liesbeek Cancer Clinic until his health failed. He was married to Myra Wahl, with whom he had a son.