Kennedy, the youngest of six children, attended Monsignor Bonner High School, from which he graduated in 1988. After attending college at various lcoations, he began performing as a bit player in movies and television shows before starting his career in stand-up comedy.
Kennedy used his voice acting skills to create a false persona, screen agent "Marty Power". Posing as Marty Power over the telephone, he attracted the attention of real agents and managers who would later book his performances. He eventually landed his first major motion picture role in the late 1990s when he was cast as Randy Meeks in the Scream series of horror films. In recent years, he has also performed minor roles in a number of other films, and most often appears opposite actor Kal Penn, including Malibu's Most Wanted, Harold & Kumar Go to White Castle, and Son of the Mask.
Kennedy formed a production company called Wannabe Producers, alongside Josh Etting, through which he has produced the shows The Jamie Kennedy Experiment, Blowin' Up, The Starlet, and Living with Fran. Following Malibu's Most Wanted (2003), which he both wrote and starred in, Kennedy co-wrote the MTV show Blowin' Up (2006) featuring his friend Stu Stone.
Kennedy lent his voice as a celebrity in the videogame ESPN NFL 2K5 as a celebrity adversary with his own football team, the Upper Darby Cheesesteaks and he is also unlockable as a Free Agent tight end in season mode. His stint as Activision's emcee at E3 2007, however, drew critics.
While working on his film Malibu's Most Wanted, Kennedy had ghostwriter Ellen Rapaport write a comic pseudo-autobiography entitled, Wannabe: A Hollywood Experiment. The book chronicles his life in Hollywood as he attempts to become a star. It gives background on his life and family, and quickly dives into his adventures. It tells of such things as Kennedy's living conditions in the Hollywood slums, his beat up car, his kidney issues, and funky characters throughout the story.
As a performer of stand-up comedy, he is best known for his sketch performances on his television reality show, The Jamie Kennedy Experiment, which became the WB Network's highest ranking new show in 2002, but which was canceled in April 2004 due to falling ratings. In 2006, Jizzy Entertainment released Unwashed: The Stand-Up Special. In 2008, Kennedy released the documentary Heckler, about the plight of stand-up comics vs their often-aggressive audience.
Since 2008, Kennedy has played psychology professor Eli James in the CBS drama Ghost Whisperer, and in real life Kennedy is dating the show's star, Jennifer Love Hewitt. He is also active in California's tourism campaign, having appeared in several commercials with Governor Arnold Schwarzenegger. Since 2009, he has been in the TV series, The Cleveland Show, playing Roberta Tubbs' boyfriend.
- Scream (1996) as Randy Meeks
- Romeo + Juliet (1996) as Sampson
- Clockwatchers (1997) as Eddie
- Scream 2 (1997) as Randy Meeks
- Boogie Nights (1997) (deleted scenes)
- As Good as It Gets (1997) as Street Hustler
- Enemy of the State (1998) as Jamie
- Starstruck (1998) as George Gordon Flynn
- Bowfinger (1999) as Dave
- Three Kings (1999) as Walter Wogaman
- Bait (2000) as Agent Blum
- The Specials (2000) as Amok
- Scream 3 (2000) as Randy Meeks
- Boiler Room (2000) as Adam
- Jay and Silent Bob Strike Back (2001) as Chaka's Production Assistant
- Max Keeble's Big Move (2001) as Evil Ice Cream Man
- Malibu's Most Wanted (2003) as Brad "B-Rad" Gluckman (lead role)
- ESPN NFL 2K5 (2004) (video game)
- Son of the Mask (2005) as Tim Avery/The Mask (lead role)
- Unwashed: The Stand-Up Special (2006) as himself
- Criminal Minds (2007) as Floyd Feylinn Ferell
- Heckler (2007) as himself
- Kickin' It Old Skool (2007) as Justin Schumacher (lead role)
- Extreme Movie (2008) as Mateus
- Reaper (2008) as Ryan the Musician
- Ghost Whisperer (2008) as Eli
- The Cleveland Show (2009) as Federline Jones (voice)
- Fanboy and Chum Chum (2009) as Kyle (voice)
- Spring Break '83 (2009) as Ballzack
- Scream 4 (2010) as Randy Meeks