Following the Armistice on November 11, 1918, members of the PPCLI Comedy Company, including McLaren, joined the Dumbells (the Canadian Army's Third Division Concert Party), which took its name from the Division's Insignia signifying strength: crossed red dumbells. The troupe continued to play shows in Europe as Canadian troops were reorganizing and returning to Britain and Canada.

In addition to the success with Canadian audiences both overseas and at home, the Dumbells became the first Canadian show to have a hit on Broadway, with their revue Biff, Bing, Bang, played the Ambassador Theatre for 12 weeks in 1921.

In "The Duchess Entertains," written by Jack McLaren, a slapstick character named "Scotty" also played by McLaren spars with a well-meaning dowager who brings party guests to visit hospitalized soldiers. After seeing his performance in this role at the Ambassador Theatre in New York, Hollywood impresario Irving Thalberg offered McLaren a screentest. McLaren declined the offer.