Mercer's career in voice work spans across both Japanese and Western animation, alongside video games. Taking over from Paul Mercier due to travel issues, Mercer is the current voice for Resident Evil character Leon S. Kennedy, having voiced him in both Resident Evil 6, and the direct-to-DVD CG animated movie Resident Evil: Damnation.
He is otherwise best known for voicing in a lot of JRPGs or anime-inspired video games, often voicing as a supporting character, if not providing additional voices. He has most notably situated himself within many of Koei's Warriors series and spin-offs, such as voicing Rei in Fist of the North Star: Ken's Rage, and Jia Chong & Taishi Ci in Dynasty Warriors 8.
Mercer has also dabbled in the occasional bit of live-action acting, including There Will Be Brawl (a live-action parody of Super Smash Bros. Brawl, that Mercer also produced and directed), where he portrayed Kirby, Meta Knight, and Ganondorf. And in Street Fighter High: The Musical as Dan Hibiki .