Nicolaas Hofmeyr Kestell, medical practitioner, was the son of John Daniel Kestell and his wife Geertruida Anna, born Hofmeyr. He passed the matriculation examination of the University of the Cape of Good Hope in 1914 and the next year passed the intermediate examination (equivalent to the first year of study) for the BA degree at the same institution. He completed the degree later, presumably through the University of South Africa, successor to the University of the Cape of Good Hope. Subsequently he qualified as a medical practitioner and practised in Johannesburg.
In 1918 Kestell was an honorary research worker at the Onderstepoort Veterinary Research Laboratories. He collaborated with H.H. Green* on the publication of a paper titled "Behaviour of bacteria towards arsenic" which was published in the 7th and 8th Report of the Director of Veterinary Research (1918, pp. 700-708). They read a paper with the same title at the annual congress of the South African Association for the Advancement of Science in 1918, which was published in the Report of the association for that year (pp. 369-374).
Kestell married Hildegarde Jakubek in Vienna, Austria. They had one daughter.