Joe Dirt (DAVID SPADE) is a mullet-topped redneck who's been picked on his entire life not only because of his looks, demeanor and name, but also because his parents abandoned him at the Grand Canyon back in 1975 when he was just eight-years-old. Now working as a janitor at radio station KXLA, Joe is suddenly put on the air with talk show host Zander Kelly (DENNIS MILLER). Mesmerized by Joe's appearance and demeanor, Zander decides to interview Joe who proceeds to tell his life story.
As Joe tells his tale of his never ending search for his parents, various flashbacks shows Joe's efforts as well as his encounters with various people around the country. They include Brandy (BRITTANY DANIEL), a young woman who befriends Joe despite him being the target of ridicule by local boy Robby (KID ROCK) and her own father (JOE DON BAKER).
Then there's Kicking Wing (ADAM BEACH), an American Indian Joe wants to hire as a tracker, but is more interested in supporting his dream of becoming a veterinarian through selling fireworks. Jill (JAIME PRESSLY) is a woman he meets at a carnival, falls for, and then worries may be his long lost sister. In New Orleans, Joe briefly works for Clem (CHRISTOPHER WALKEN), a school custodian with a checkered past, and then later meets Charlene (ROSANNA ARQUETTE) who runs a gator farm.
As Joe continues telling his story to Zander over the radio and recounts meeting others and holding down a variety of odd jobs, he soon becomes something of a celebrity, all while still trying to find his parents and figure out why they left him so many years ago.