Justin Bartha: The 29-year-old, who stars as the computer whiz opposite Nicolas Cage, calls his path from college to ‘Gigli’ to ‘National Treasure’ an ‘odd progression.’

“I feel like I’ve had a few careers already,” said Justin Bartha.

The 29-year-old was sitting in the kitchen of the cottage he just bought above Laurel Canyon, dressed in a porkpie hat, long-sleeve shirt, jeans and moccasins. Bartha immediately apologized about his cold, offering a fist tap instead of a handshake.

Inside, his house was freezing and empty -- a bachelor pad cum work-in-progress. Bartha handed out bottled water before sitting in his kitchen to discuss his unusual career -- high school theater in West Bloomfield, Mich., college drama and film at NYU, followed by his first big break -- “Gigli.”

“It’s an odd progression,” he admitted of his rise from there to here.

Here is playing Nicolas Cage’s sidekick in the Disney franchise “National Treasure.” The rise to success was sudden but hardly steady -- given that this new career was launched by “Gigli,” that infamous bomb of 2003, written and directed by Martin Brest and starring then “it” couple Ben Affleck and Jennifer Lopez.

There was, too, an HBO political film, “Strip Search,” in which Bartha was directed by another film giant, Sidney Lumet.

But back, of course, to “Gigli,” that punchline to a thousand easy jokes. Bartha couldn’t help defending Brest, explaining that the director shot a dark-toned, substantial movie that was lightened and butchered, after the fact, to coincide with Affleck and Lopez’s budding star love. Despite the cataclysmic reviews, “Gigli” was good to Bartha; in his first paid job, he was the third lead, playing the mentally disabled Brian, whom Affleck’s character takes hostage.

“I feel like I’ve had a few careers already,” he said.

Bartha spent several months volunteering in a program for people with mental disabilities to prepare for “Gigli.” No such actorly preparation was needed for “National Treasure,” and the results have been considerably more triumphant.

The actor recently returned from being flown around the world to promote the sequel, which Disney hopes continues “National Treasure” as a fun, and lucrative, PG adventure franchise. The new one, dubbed “Book of Secrets” and due out Friday, finds Bartha again playing the computer-whiz sidekick Riley Poole to Nicolas Cage’s braniac explorer of American antiquity, Ben Gates.

The first “National Treasure” began with Ben and Riley stealing the Declaration of Independence; “Book of Secrets” involves Ben trying to clear his family’s name from involvement in the assassination of President Lincoln by John Wilkes Booth. Riley, of course, gets dragged along. Cage’s Ben is not only brave but fussy and passive-aggressive about historical factoids and ephemera; to watch the movie is to feel as though you’re playing Trivial Pursuit with someone who loves to lord it over you with his breadth of knowledge.

Maybe that’s why Riley is such easy, and winning, comic relief. He needles Ben about his annoying ticks while helping him track down treasure, disabling alarms, hacking into computer systems and flying a robotic surveillance helicopter around the Eiffel Tower. The crux of his character, Bartha said, “is making him the audience member being pulled up and thrown into this adventure.”

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Where you’ve seen him

Justin Bartha, who studied acting and film at NYU, got his first role in “Gigli,” a performance producer Jerry Bruckheimer saw before casting Bartha in “National Treasure.” He also appeared in NBC’s “Teachers,” a short-lived sitcom that aired two seasons ago. Coming up is a romantic comedy, “Shoe at Your Foot.” He also hopes to make “Holy Rollers,” about Orthodox Jews in the Ecstasy trade.