Killam joined the cast of MADtv as a featured player during its seventh season from 2001 to 2002. Of the 25 episodes that aired during MADtv's seventh season, Killam appeared fully in 13 episodes. Joining the MADtv cast at age 19, Killam was the youngest cast member hired on the show and the only cast member on MADtv to get his start on children's shows (similar to Kenan Thompson on Saturday Night Live). He was a regular cast member on the third and fourth seasons of Nick Cannon's Wild 'N Out. In 2005, Killam co-starred in the television pilot Nobody's Watching, which never aired on network TV. The pilot gained popularity after it was leaked online and webisodes were produced from 2006 to 2007.