Cox replaced George Eads in the role of Captain Atom for the popular superhero cartoon Justice League Unlimited. Eads was unwilling to reprise his voice role after an appearance in Unlimited's first episode, so the producers chose Cox as a replacement. In the Justice League Unlimited third season episode "Patriot Act", Chris returned to play a different Justice League member, the Shining Knight.
Cox has also provided a number of voices for Seth MacFarlane's animated series Family Guy and American Dad!, including that of American President George W. Bush, as well as Principal Goodvibes in The Grim Adventures of Billy & Mandy.
Cox is also the voice of Pecker in the Jak and Daxter series of video games from Jak II onwards, as well as the voice of Sergei Voronov in the video game Mercenaries: Playground of Destruction. He has also played more minor roles in games such as Metal Gear Solid 3: Snake Eater, Killer7 and Dark Sector.