Returning to Canada in 1905, Thomson worked at a succession of commercial design firms in Toronto. At The Grip Limited, he found himself with colleagues who were also highly trained fine artists, and saw potential in this reticent new employee. Thomson was encouraged and mentored by J.E.H MacDonald, Arthur Lismer, Fred Varley, all future members of the Group of Seven. Lawren Harris, A.Y. Jackson and Franklin Carmichael also became part of Thomson’s circle. When art patron Dr. James MacCallum saw Thomson’s early sketches, he offered financial support which allowed Thomson to quit commercial art and devote himself to painting full time.