He studied under Morris Zaslow, the senior northern historian in the country at the time, at the University of Western Ontario, receiving his PhD in 1973.
His thesis was entitled, "The Mounted Police on Canada's Northern Frontier, 1895 - 1924."
After a short stint with the National Historic Sites Service in Ottawa, Morrison was hired at Brandon University in 1969, remaining there until 1989.
Morrison received an honorary degree (Doctor of Literature) from Brandon University in 2007.
Among his best known works are True North: The Yukon and Northwest Territories (Oxford, 1998), The Alaska Highway in World War II (University of Oklahoma Press, 1992), The Sinking of the Princess Sophia: Taking the North Down With Her (Oxford, 1991), Land of the Midnight Sun: A History of the Yukon revised edition (McGill-Queen's University Press, 2005),[2] and Showing the Flag, The Mounted Police and Canadian Sovereignty in the North, 1894 – 1925 (UBC Press, 1985).