He is best known for his voice roles as Donatello in the 2003 Teenage Mutant Ninja Turtles series and Phoenix Wright in the Ace Attorney games.

Since 2015, he has been a regular cast member of the web series Critical Role, in which he and other voice actors play Dungeons & Dragons.

He also had television roles on Guiding Light and Another World as a teenager, but opted to pursue a career onstage over screen acting as he preferred the live feedback of a theater audience.

[11][17] In November 2019, Amazon Prime Video announced that they had acquired the streaming rights to this animated series, now titled The Legend of Vox Machina.

[19] He hosts the All Work No Play podcast and spinoff web series with his Critical Role co-star and best friend Liam O'Brien.

[27] In July 2024, Riegel revealed that he had been diagnosed with HPV-positive oropharyngeal cancer earlier in the year and was recovering after undergoing six weeks of radiation therapy and surgery to remove his tonsils alongside parts of his tongue and soft palate, leaving him with a seven-inch scar across his throat.