Born 27 July 1882 at Anowtown, Central Otago, New Zealand, he was educated at Otago Boys High School and Otago University where he qualified in 1906. He then came to England for two years, and after taking the Fellowship returned to practice at Gore, Southland. He soon moved to Dunedin, where in 1915 he became assistant surgeon to the Public Hospital under Professor Sir Louis Barnett. He was at the same time surgical tutor and lecturer in surgical anatomy at the Medical School, and during the war carried out much military surgery and founded a physiotherapy department for rehabilitation of ex-soldiers. After the war he made postgraduate studies in London and then specialised in ophthalmology and in the surgery of the ear nose and throat. Back in Dunedin he succeeded A J Hall in the ENT department and, in 1937, Sir Lindo Ferguson in the eye department of Dunedin Hospital. He also lectured on these subjects in the University. He retired from all these posts in 1945 but continued in active practice at 211 High St, Dunedin, till 1957. He was the first local President of the Hard of Hearing League, and a founder member of the New Zealand Ophthalmological Society and afterwards its President. He was a foundation Fellow of the Royal Australasian College of Surgeons and examined in ophthalmology for its Fellowship. Carswell was an assiduous reader and an excellent teacher, unassuming, generous, and cheerful. His recreations were trout-fishing, ornithology, and billiards at the University Club of which he was a founding member in 1923. He died on 19 September 1958 in Dunedin and his widow, Eleanor Ann (MacGibbon), died unexpectedly a few weeks later at Christchurch. Their two married daughters and their son, William Roy Carswell MC, FRCS of Palmerston North, survived them.