Marmel had been stand-up comedian since the age of 18, and was discovered while performing in 1996 by a Hanna Barbera executive who thought he'd be ideal as a writer for Johnny Bravo. He has since worked on numerous other shows for Hanna Barbera, Nickelodeon and Disney Channel, and has been nominated for multiple Emmy and Annie Awards for his work as a writer, producer and songwriter.
Marmel grew up in Lincolnwood, Illinois and is an alumnus of the University of Wisconsin, where he majored in journalism. Marmel and his wife currently reside in Los Angeles.
Marmel, regarding his political views, describes himself as a "raging moderate". The conservative magazine The American Spectator praised Marmel's depiction of conservatives in the animated TV series This Just In!, while second amendment advocates have criticized Marmel's support of gun control.