Robert Eustace Montgomery graduated (MRCVS) in 1903 at the Royal (Dick) Veterinary College in Edinburgh, Scotland. After special duty in India and Canada he was sent in 1907 by the Liverpool School of Tropical Medicine to investigate sleeping sickness (in both humans and domestic stock) in central Africa. The results of his investigation were reported in several papers in the Annals of Tropical Medicine (1908-1909). In 1909 he was appointed as pathologist to the East African Protectorate and in the same year attended the Pan-African Veterinary Congress held in Pretoria to mark the official opening of the Veterinary Research Institute at Onderstepoort. Also in 1909 he contributed a paper, "Trypanosomes and their transmission (Fly Disease) in relation to South Africa", to the Proceedings of the Rhodesia Scientific Association (Vol. 9, pp. 14-39). He visited South Africa again in 1912 in connection with the immunisation of cattle against East Coast Fever. During World War I (1914-1918) he served with the rank of Major in the East African Veterinary Corps. In 1917 he started the veterinary institute at Kabete in Kenya and when Sir Arnold Theiler* resigned in 1918 he succeeded him as Director of Veterinary Research for the Union of South Africa.
However, after an extensive tour of South Africa and six month's leave, he returned to East Africa in March 1920 and Theiler was re-appointed. From 1923 to 1926 he served as veterinary adviser to the governments of Kenya, Uganda and Tanganyika, and from 1930 until his death in the same capacity to the Colonial Office.
Montgomery was the first president of the South African Veterinary Medical Association in 1920-1921. He became a member of the South African Association for the Advancement of Science in 1918 and that same year was elected a member of its council for 1918/9. In 1920 he was a member also of the South African Biological Society.