His roles include Wakko Warner in Animaniacs, Captain Hero in Drawn Together, Jerry in the first two seasons of Totally Spies!, Ironhide in the first three Transformers films directed by Michael Bay, the titular character in the Crash Bandicoot franchise, and Wooton Bassett in Adventures in Odyssey.

[2][3] In 1989, Harnell provided the voices of Br'er Rabbit and many other critters for the Splash Mountain attraction at Disneyland Park.

He has continued to reprise the role of Brer Rabbit in new Disney projects when needed, such as in the 2011 video game Kinect: Disneyland Adventures.

[4] From 1994 to 1996, he supplied the voices of Sewer Urchin, the Human Bullet and Chief Louder in the animated series The Tick.

He also voiced Captain Hero on Comedy Central's animated comedy Drawn Together and he also does the voices of Wooton Bassett and Bennett Charles on the radio drama Adventures in Odyssey,[5] as well as playing the lead role of Finnian Jones for the Lamplighter Theatre Radio Drama.

He also produced the 2004 film Comic Book: The Movie along with Billy West, Mark Hamill, Eric Mittleman, Scott Zakarin and Roger Rose as well as playing the character Ricky.

He also voiced Flip Wreck, Blast Zone and Bucko in the Skylanders reboot of the franchise and Cowardly Lion and Reegull in Lego Dimensions.