Thicke was born in Kirkland Lake, Ontario, Canada, the son of Shirley "Joan" Isobel Marie (née Greer), a nurse, and William Jeffery, a stockbroker. They divorced in 1953. His mother remarried to Brian Thicke, a physician, and they moved to Elliot Lake.

Thicke graduated from Elliot Lake Secondary School in 1965, and was elected homecoming king. He went on to attend the University of Western Ontario, where he joined the Delta Upsilon fraternity.