As a youth, he worked as a copy boy at the Pittsburgh Leader and helped to distribute publicity material for concerts that his mother arranged.

During subsequent winters he acted in plays that included Shavings and The Emperor Jones.

[3] Following his West Coast performance in The Rivals, Thomson declined a contract offer to work in films from Cecil B. DeMille, Returning to New York, Thomson acted in Hush Money with Henry Miller's company., following which he accepted a two-year contract offer from DeMille.

[3] Thomson and his wife, Alden Gay, were founding members of the Screen Actors Guild.

[6] After appearing in several Broadway plays during the early and mid-1920s, Thomson would make his film debut with a starring role in 1926's Risky Business.