Posehn performed the voice of Gibbons, a tiny man, on several episodes of the Cartoon Network's Tom Goes to the Mayor (2005–2006). He also appeared in the 2005 pilot for The Showbiz Show with David Spade, in a segment called "The Nerd Perspective", in which he gave a scathing criticism of MTV and its declining quality. He also played a mortician in several episodes of Comedy Central's Reno 911!. He was featured on the 2005 documentary series The Comedians of Comedy on Comedy Central and Showtime. He was in a 2007 episode of the improv series Thank God You're Here on NBC and was a Celebrity judge on the revived 1970s game show The Gong Show with Dave Attell (2008), on Comedy Central. He co-stars on The Sarah Silverman Program with Steve Agee as a gay couple who is friends with Silverman, and also wrote the season three finale "Wowschwitz". He played himself in the episode "Spagett" of Tim and Eric Awesome Show, Great Job!, appeared at the Comedy Central Roast of Bob Saget, played the role of a physically disabled man (Scooter Man) in the second season's premiere episode "Slip of the Tongue" of Californication (2008), on Showtime, and played Dethklok's second manager in the Metalocalypse episode "Dethsources", he also wrote the episode "Fatherklok". In 2007 he joined the first season of the MTV Sketch comedy series Human Giant, as a Writer and performer, and voices Glen Furlblam, the biggest fan of Dr. Two-Brains on the PBS Kids animated series WordGirl. In 2012 he co-wrote the fourth season of Metalocalypse. Since 2013, Posehn has appeared in the recurring role of Bert on The Big Bang Theory.