Franco was born in Palo Alto, California to Doug Franco and Betsy Levine Verne (a poet, author and editor); his maternal grandmother runs the Verne Art Gallery, a prominent art gallery in Cleveland, Ohio. Franco's father is of Portuguese and Swedish descent, while his mother is Jewish, a descendant of immigrants from Russia.
He grew up in California with his two younger brothers, Tom and David, and graduated from Palo Alto High School in 1996, where he was elected by his senior class as the boy with the "best smile". He then enrolled at the University of California, Los Angeles as an English major, and studied acting. Much to the disapproval of his parents, he dropped out after his freshman year and chose to pursue a professional career as an actor, taking acting lessons with Robert Carnegie at Playhouse West. After fifteen months of training, he began auditioning in Los Angeles, California and got his first break in 1999, after he was cast in a leading role on the short-lived but well-reviewed television series Freaks and Geeks. Franco has since described the series as "one of the most fun" work experiences that he has had.
Franco's first major film was the romantic comedy Whatever It Takes (2000). He was subsequently cast as James Dean in director Mark Rydell's 2001 biographical TV film of the same name. The role brought Franco much critical acclaim, and he was distinguished in 2002 with a Golden Globe Award, as well as nominated for an Emmy Award and a Screen Actors Guild Award. After seeing him in James Dean, actor Robert De Niro handpicked Franco to play his son in the drama City by the Sea.
Franco was originally considered for the lead role of Peter Parker in the film version of Spider-Man, but was instead cast in the supporting role of Harry Osborn, the son of the villainous Green Goblin. Both Spider-Man (2002) and Spider-Man 2 (2004) were very well-received critically and commercially, and Franco has since co-starred with Neve Campbell in The Company (2003).
In 2006, Franco co-starred with Tyrese Gibson in Annapolis and played legendary hero Tristan in Tristan & Isolde, a dramatisation of the Tristan and Iseult story also starring English actress Sophia Myles. He trained with the stunt team "The Blue Angels" and received a pilot's license in preparation for his role in Flyboys, which was released in September of 2006; the same month, Franco appeared briefly in The Wicker Man, a horror film starring Nicolas Cage (who directed him in Sonny).
Franco's next role will be in Spider-Man 3, currently scheduled for release on May 4, 2007. He is scheduled to star in several other films due for a 2007 release, including Pineapple Express, a comedy co-starring Seth Rogen and written and produced by Judd Apatow, both of whom worked with Franco on Freaks and Geeks.
Franco lives in Los Angeles. Franco, who was chosen by People magazine as one of the 50 Hottest Bachelors of 2004, paints extensively in his free time and even attended a private painting school during his teen years. His works have already been displayed in art galleries in and around Los Angeles.
In 2006, Franco was named one of Salon.com's "10 men who might just inspire the rebirth of Jewish male cool"-Franco is half Jewish.