Willingham rose to fame in the voice acting world for his portrayal of Roy Mustang in Fullmetal Alchemist and reprised the role in Fullmetal Alchemist: Brotherhood. His roles include Yu Kanda in D. Gray-man, Cleo in Glass Fleet, Ginko in Mushishi, Portgas D. Ace in the Funimation re-dub of One Piece and Takashi Morinozuka in Ouran High School Host Club. He also voices Thor in several Marvel projects and King Roland II in Disney Junior's Sofia the First. Between 2010 and 2018, he was the voice of Knuckles the Echidna from the Sonic the Hedgehog series. He is a cast member of Critical Role, a web series in which voice actors play Dungeons & Dragons.