After qualifying in 1903, he held house appointments at the East London Hospital for Children, and then studied psychiatry in Paris and Zurich.
At the beginning of WWI he joined the RAMC with the rank of major and served as lecturer in mental disease at Moss Side Military Hospital, Maghull, where veterans with shell-shock were treated.
[2] Upon the founding of The Journal of Neurology and Psychopathology in 1920, he was one of the nine members of the editorial committee, headed by Samuel Alexander Kinnier Wilson.
Hart's 1910 paper The conception of the subconscious introduced the works of Janet and Freud to English-speaking psychologists.
[2] During the second world war he was chief adviser on psychiatric matters to the Emergency Medical Service, working in close partnership with Gordon Holmes.