John Wallace Weir qualified as Doctor of Medicine (MD) at the University of Edinburgh in 1880 and as a Fellow of the Royal College of Surgeons of Edinburgh in 1886. He was licensed to practice in the Cape Colony on 22 September 1887. By 1893 he had settled at Engcobo in the Transkei and was still there in 1915. He was a member of both the Cape of Good Hope Branch of the British Medical Association and the [second] South African Medical Association. By 1897 he was visiting surgeon at the Emjanyana Leper Institution at Idutywa. During the first decade of the twentieth century he published several papers in the South African Medical Record: "Notes on leprosy in the native territories" (1904), "Notes on Kaffir medical practice" (1904), "Some thoughts on the leprosy controversy" (1907), and "Leprosy in South Africa - historical facts" (1909, in two parts).
By 1926 Weir was living in East London. He should not be confused with his contemporary James Wilson Weir, who was a merchant at King William's Town.