Jamie Kennedy, the youngest of six children, was born in Upper Darby, Pennsylvania to a machinist father and an accountant and paralegal mother and was raised Catholic. He attended and graduated from Monsignor Bonner High School in 1988. After studying acting in college, he began his career as a Hollywood extra and honed his skills at voice impersonations.

This skill led to, among other things, an unorthodox success in the way of creating a false persona, screen agent "Marty Power" (a fictitious person). Posing as Marty Power over the telephone, Kennedy attracted the attention of real agents and managers who would later book his performances. He eventually landed his first major motion picture role in 1996 when he was cast as Randy Meeks in the Scream trilogy of horror films. 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.  In 2006, he released Unwashed: The Stand-Up Special.

He formed a production company called Wannabe Producers with Josh Etting through which he has produced the shows The Jamie Kennedy Experiment, Blowin' Up as well as The WB shows 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. While working on Malibu's Most Wanted, Kennedy had ghostwriter Ellen Rapaport write a pseudo-comedic 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.

He has also performed minor roles in a number of other films. 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.