Herman was part of the original cast of the late-night FOX sketch show MADtv in 1995 and lasted there until the first half of season three, when he wanted to leave for other projects, but FOX wouldn't let him out of his contract, since the show already lost Artie Lange (who was fired due to his erratic behavior from cocaine abuse and being found in a car dressed as a sow and doing coke during rehearsal for a sketch called Babewatchnote ). In retaliation, Herman decided to scream all of his lines during one of the show's read-throughs. Unlike most of the cast at the time, David Herman (along with Phil LaMarr, to a lesser extent, since LaMarr was in the movie Pulp Fiction) was the only cast member who had an established acting career prior to being a cast member.
Herman's recurring characters on MADtv include Mike Lawson (the host of an infomercial show called Incredible Findings), Marsh (the anchor to a news program called Gen X News), and Joel Linder (a concerned father). His celebrity impressions include: Don Adams (as Maxwell Smart from Get Smart), Tim Allen (as Tim "the Tool Man" Taylor from Home Improvement), Woody Allen, Nicolas Cage, Bill Clinton, Bob Dole, David Duchovny (as Fox Mulder from The X-Files), Larry Flynt, Tom Hanks (as the title character from the movie Forrest Gump and as Jim Lovell from Apollo 13), Larry King, Kenny Kingston, Regis Philbin, Charles Nelson Reilly, John Ritter (as himself and as Jack Tripper from Three's Company), Joel Schumacher, Robert Shapiro, Pauly Shore, Brent Spiner, Patrick Stewart (as Jean-Luc Picard from Star Trek: The Next Generation), and Alex Trebek.
After MADtv, Herman did voice-acting, provided roles in animated shows such as Futurama, Disenchantment, Bob's Burgers, Brickleberry (as narcissistic and dangerously idiotic park ranger, Steve Williams), its Spiritual Successor, Paradise PD (as Officer Kevin Crawford, who is incompetent like Steve Williams, but not to ludicrous degrees); and King of the Hill (various roles, though David Herman usually plays wussy, nonconfrontational men, like Eustace, Hank's old friend from the Straight Arrow Scouts who was kicked out for breaking the vow of silence; or Anthony Page, the social worker who accused Hank of being a child abuser in the pilot episode [and later, was a caseworker for a drug addict who got his addiction put down as a disability in order to get hired at Strickland Propane]. The only exception to this is Jimmy Witchard, who is an angry, mentally retarded man with a history of violence and petulant childish behavior). Herman was also featured in two of Mike Judge's live-action cult films: Office Space and Idiocracy.
- Office Space: Michael Bolton.
- MADtv: Various roles. See above
- Best Fiends: Roger the Slug, Gordon the Scorpion
- Bob's Burgers: Mr. Frond, Marshmallow
- Disenchantment: The Herald, Prince Guysbert, Jerry, Chazz, Sven, Hansel, The Griffin, Old Man Touchy, and many others.
- Futurama: Scruffy the janitor, Professor Wernstrom, Mayor Poopenmeyer, Larry (one of Mom's sons), Roberto (the mentally deranged criminal robot), Fatbot, Malfunctioning Eddie, Turanga Morris (Leela's father), and many others.
- OK K.O.! Let's Be Heroes: Mr. Gar (probably the only character David Herman has voiced who's considered traditionally manly)
- Scooby-Doo! and the Curse of the 13th Ghost: The Sheriff
- Scooby-Doo: Return to Zombie Island: The Sheriff, Jack