Born on 24 March 1865 at Wellington, New Zealand, the son of Alfred A Barnett, JP. He was educated at Wellington State School and College, and at Otago University, Dunedin. He made his medical studies at Edinburgh where he graduated, and at the Middlesex Hospital where he served as house surgeon. After taking the Fellowship in 1890 he went back to New Zealand, and was elected surgeon to the Dunedin Hospital. He was appointed university lecturer in surgery in 1895, becoming professor in 1909; and retiring in 1925 with the title of emeritus professor. During the war of 1914-18 he was a consulting surgeon with the New Zealand Expeditionary Force with the rank of lieutenant-colonel, and was created CMG for his services. Barnett took a leading part in professional gatherings. He was president of the surgical section of the sixth Intercolonial Medical Congress at Hobart in 1902, president of the New Zealand Medical Association in 1907, and president of the second Australasian Medical Congress of the second series, when it met at Dunedin in 1927. He was vice-president of the section of surgery at the British Medical Association's centenary meeting in London in 1932. He was a foundation Fellow of the Royal Australasian College of Surgeons and its president in 1937, and had in fact been its prime founder. Barnett was active in encouraging medical research and in awakening public interest in it. He founded the Dunedin Radium Institute, and was a Vice-president of the New Zealand Cancer Campaign, and also served as chairman of the Otago and Southland division of the British Empire Cancer Campaign; he was, too, chairman of the New Zealand hydatid research committee. Barnett married in 1892 Mabel Violet, daughter of the Hon James Fulton, a member of the New Zealand legislative council. One of their sons, Geoffrey Barnett, FRCS (1893-1950), practised as a surgeon at Dunedin. Barnett died at Dunedin on 28 October 1946, aged 81. He had lived latterly at Hampden, Otago.