Born in St. James, Barbados, Clarke had his early education there and taught at a rural school for three years. In 1955 he moved to Canada to attend the University of Toronto but after two years turned his hand to journalism and broadcasting.
He was a reporter in the Ontario communities of Timmins and Kirkland Lake, before joining the Canadian Broadcasting Corporation as a freelance journalist. He subsequently taught at several American universities, including Yale University (Hoyt fellow, 1968–70), Duke University (1971-72), and the University of Texas (visiting professor, 1973).
In 1973 he was designated cultural attaché at the Barbadian embassy in Washington, DC. He was later General Manager of the Caribbean Broadcasting Corporation in Barbados (1975-1977). Returning to Canada, in 1977 he ran as a Progressive Conservative candidate in the Ontario election. He was writer in residence at Concordia University, Montreal, Quebec (1977), and at University of Western Ontario (1978). From 1988 to 1993 he served on the Immigration and Refugee Board of Canada.
In September 2012, at the International Festival of Authors (IFOA), Clarke was announced as the winner of the $10,000 Harbourfront Festival Prize "on the merits of his published work and efforts in fostering literary talent in new and aspiring writers". Previous recipients of the award (established in 1984) include Dionne Brand, Wayson Choy, Christopher Dewdney, Helen Humphreys, Paul Quarrington, Peter Robinson, Seth, Jane Urquhart and Guy Vanderhaeghe.
Clarke was reported as saying:
"I rejoiced when I saw that Authors at Harbourfront Centre had named me this year's winner of the Harbourfront Festival Prize. I did not come to this city on September 29, 1959 as a writer. I came as a student. However, my career as a writer buried any contention of being a scholar and I thank Authors at Harbourfront Centre for saving me from the more painful life of the 'gradual student.' It is an honour to be part of such a prestigious list of authors.