Stewart made his TV debut as Razor Dee, a spaced-out DJ on the syndicated "The New WKRP in Cincinnati" (1992-1993). He also appeared in guest spots on "Seinfeld", "The Larry Sanders Show", as the weird intern, and had a recurring role in the CBS sitcom "The Boys Are Back". He was then cast as the most childlike of aliens in "3rd Rock". Playing brilliantly off fellow cast members (notably John Lithgow and Kristen Johnston), Stewart showed a gift for physical comedy ("Harry is a broad-based character drawn from silent films, of which I have a huge collection").
Thus far, Stewart's involvement in film has been minor. His first role was as a lieutenant in the sci-fi thriller "Stargate" (1994) followed by bit parts in "Leaving Las Vegas" (1995) and "Broken Arrow" (1996). He had better roles in independent films, including the leads in the low-budget WWII drama "The Poison Tasters" and the frat-house comedy "Glory Daze" (both 1995). Since his TV success, Stewart has garnered the much larger supporting role of Happy in "McHale's Navy" (1997).