A. Marius Wilson, medical practitioner, was the son of J.B. Wilson, a teacher at the South African College, Cape Town. Marius went to Durham, England, to study medicine and qualified as Bachelor of Medicine (MB) and Bachelor of Surgery (BS) in 1891. The next year he was admitted as a member of the Royal College of Surgeons of England (MRCS) and a licentiate of the Royal College of Physicians of London (LRCP). Continuing his studies at the University of Durham and St Thomas Hospital he qualified as Doctor of Medicine (MD) in 1893. That same year he published Myxoedema, and the effects of climate on the disease, which was presumably based on the research for his doctorate. For a short time he served as medical officer of health at the Port of Colchester. He became a member of the British Medical Association and was elected an honorary life member of the St John Ambulance Association. In later years he was elected a Fellow of the Royal Society of Medicine (London), and of the Royal Institute of Public Health.
Upon returning to Cape Town Wilson was licensed to practice medicine in the Cape Colony on 11 April 1894. After a few years he moved to premises in Hof Street, Cape Town, where he remained to the end of his career. He served as medical officer to the Cape Government Railways and later the South African Railways, was a visiting physician at Somerset Hospital and visiting surgeon at All Saints' Homes, Cape Town, and was a member of the Colonial Medical Council for twelve years. During World War I (1914-1918) he was on active service with South African forces as a major in the Royal Army Medical Corps. His publications included papers on "Two cases of obscure aortic aneurysms" (British Medical Journal, 1908), "Case of a ruptured heart" (Lancet, 1908), "Nutmeg poisoning" (Transactions of the Royal Society of South Africa, 1910), "The nymphae" (Anthropological Transactions of the South African Medical Congress, 1910), "Short note on the treatment of malaria" (Transvaal Medical Journal, 1912), and "Quinine and malaria" (South African Medical Record, 1919).
Wilson was a member of the (second) South African Medical Association by 1898. He became a member of the South African Philosophical Society in 1903 and was elected one of the founding Fellows of its successor, the Royal Society of South Africa. He later served on the council of the latter society for 1916. By 1903 he was a life member of the South African Association for the Advancement of Science.