Knoxville was born in Knoxville, Tennessee, the son of Lemoyne and Philip Clapp, who was a car salesman.
Knoxville credits a copy of Jack Kerouac's On the Road given to him by his cousin, country singer/songwriter Roger Alan Wade, with giving him the acting bug. After graduating from South-Young High School in 1989 in Knoxville, he moved to California to become an actor, and at first appeared in commercials and as an extra. Not getting the big break he had hoped for, he began writing and pitching article ideas to various magazines. An idea to test self-defense equipment on himself was picked up by the Jeff Tremaine-helmed skateboarding magazine Big Brother, and the stunts were filmed and included in Big Brother's Number Two video.
Eventually, Knoxville, Tremaine, Sean Cliver and Dave Carnie produced a pilot that used Big Brother footage along with footage from Bam Margera's CKY videos, and with help from Tremaine's friend, film director Spike Jonze, they pitched a series to various networks. A deal was made with MTV and Jackass was born. Knoxville also participated in the Gumball 3000 for Jackass along with co-stars Steve-O, Chris Pontius, Jackass director Jeff Tremaine, and producer Dimitry Elyashkevich. Prior to Jackass landing on MTV, Knoxville and company turned down an offer from Saturday Night Live to perform similar stunts for the show on a weekly basis (Knoxville eventually did host SNL in 2005).
