George Gray Hay, medical practitioner, was the son of Alexander Hay and his wife Margaret Ann, born Fraser. He qualified as Bachelor of Medicine (MB) and Bachelor in Surgery (ChB) in Edinburgh in 1899. By 1903 he had arrived in South Africa, for in that year he was registered as a medical practitioner in the Transvaal Colony, was appointed as district surgeon of Louis Trichardt (now Makhado), and reported on the sanitation of the town. He remained there for some 25 years, though in 1905 he was also justice of the peace at Klein Spelonken, in the Pietersburg (now Polokwane) district. In 1928 he was appointed as special justice of the peace at Messina (now Musina), but he resigned this post the next year.
During World War I (1914-1918) Hay began writing some pamphlets on the prevention of malaria. These were issued separately in Dutch and English by the South African Anti-Malarial Association in Johannesburg: Fever on the farm, some common causes (1914); First measures in malaria prevention for farmers and settlers (1915; revised ed. 1924); and Malaria prevention on active service. Notes for the information and guidance of the Union troops on service in Central and East Africa (1916). An article by him on "Amaas" [or alastrim, a specific contagious eruptive fever resembling smallpox] was published in the South African Medical Journal (1938, Vol. 12, p. 639) in the year of his death.
Hay was married in Polokwane to Marian Catherine Grieve, with whom he had a son and a daughter.