Born on 10 January 1870, he was educated at the London Hospital and qualified in 1901 when he was 31. He won a surgical scholarship (1901) and served as house surgeon to Sir Frederick Treves and Jonathan Hutchinson junior at the London, and then was resident medical officer at the West Ham Hospital, now Queen Mary's Hospital for the East End, 1901-07. After taking the Fellowship he was promoted to the surgical staff of the hospital and served various other east London hospitals. He lived at 343 Romford Road, Forest Gate and was chairman of the Stratford division of the British Medical Association 1931-33. He had consulting rooms in Wimpole Street. He retired in 1933, but kept a little practice and returned to full activity during the war of 1939-45 as casualty officer at King George Hospital, Ilford, where he had been consulting surgeon for many years. Couzens never married; though reticent and shy, he had a large circle of friends. He was a keen golfer and addicted to motor-cars. He died in a nursing home at Hatch Beauchamp, Somerset on 22 November 1959 aged 89. He left £1500 to the Royal National Institute for the Blind, stating "I do not wish my name to be associated in any way with the bequest."