He has had guest appearances in a number of television shows and movies. He is perhaps best known for six seasons as a regular on Mad TV and for his small role as Marvin, the man whom John Travolta accidentally shoots in the face in Pulp Fiction.
LaMarr is also a prominent voice actor in video games and animated series like Justice League (as Green Lantern John Stewart), Justice League Unlimited, Futurama (as Hermes), Samurai Jack, The Weekenders (as Carver), Invader Zim (as Poop Dogg), Family Guy, Foster's Home for Imaginary Friends (as the basketball-obsessed imaginary friend named Wilt), and Static Shock (as Static). He has also voiced for the video games Jak II and Jak 3 of the Jak and Daxter series, Metal Gear Solid 2 (as Vamp), Star Wars: Knights of the Old Republic (as Gadon Thek), and Mercenaries.
- LaMarr was an extra in Spider-Man 2. This is unusual as extras often have little to no acting experience.
- Static Shock and Justice League have had a few crossovers where the characters Green Lantern and Static shared scenes. As the voice actor of both superheroes, LaMarr is literally talking to himself.