As Dean of the Faculty of Medicine at University of Toronto, he oversaw creation of the Department of Psychiatry, and development of the medical school.

Clarke was an early proponents of eugenics, emphasizing the importance of restrictive laws that would limit the immigration and marriage of the "mentally defective."

To them, such laws seemed necessary to stem the explosive growth of state and provincial mental asylums where foreign-born patients made up more than 50 percent of the hospital population.

By 1905, Clarke had abandoned the movement, and many of the other leading psychiatrists would follow suit by the end of World War I, when it was clear that eugenic measures were not having the desired effects.

Three of his sons were active as ice hockey players on professional or amateur levels in Canada and the United States.