J. Withers Gill was a Fellow of the Royal Geographical Society. He lived in Bulawayo, in present Zimbabwe, at the start of the twentieth century and played an active role in the Rhodesia Scientific Association (founded in 1899). In February 1900 he exhibited objects found at the Khami Ruins and photographs at a meeting of the association, and in July again exhibited ornaments found there. He delivered a paper in April that year, entitled "Notes on a comparison between the ruins at the Khami River and at Zimbabwe", which was published in the association's Proceedings (Vol. 1, pp. 9-10). In March 1900 he was elected a member of the association's council, serving as honorary treasurer. At the annual general meeting in July 1901 he was elected joint vice-president and re-elected to that position for 1902/3.
He is probably the same person as J. Withers Gill, Officer of the Order of the British Empire (OBE), later of the West African Political Service, who wrote 'Hausa speech, its wit and wisdom' (Bulletin of the School of Oriental and African Studies, 1918), A short history of Salaga (Accra, 1924) and The Moshi tribe: A short history (Accra, 1924).