“I grew up watching lots of movies, but I had never been much into theater,” says Isaac, 33, who was born in Guatemala and raised in Miami. “But when I walked out of that play, I was thinking ‘Oh my God. This is what I want to do. This is it.’ ”

Isaac had been singing and playing lead guitar for a local band, but his artistic passion shifted. He started auditioning for Area Stage director John Rodaz and got cast in small roles. He landed a bit part in the made-in-South Florida crime-drama Illtown. During a trip to New York, he walked by the prestigious Juilliard School, filled out an application and was accepted. He graduated in 2005 and started to work steadily, going from small roles in All About the Benjamins and Law & Order to bigger but still supporting roles in more prestigious pictures such as Drive, Sucker Punch, The Bourne Legacy and Ridley Scott’s Robin Hood.

But after Inside Llewyn Davis, which opens Friday, everyone in Hollywood will know Isaac’s name. The actor does all his own singing and guitar-playing in Joel and Ethan Coen’s melancholy comedy about the eponymous musician, who wows crowds at Greenwich Village pubs and coffeehouses in 1961 New York but hasn’t made a dime off the self-produced album he released after his former singing partner committed suicide. Llewyn is so broke that he’s homeless. He bounces around his friends’ couches to sleep at night, can’t afford a proper winter coat and has trouble connecting with people. His sister resents him, his aging father is uncommunicative and his ex-girlfriend (Carey Mulligan), a singer who is now married to another musician (Justin Timberlake), is furious at him for getting her pregnant during a one-night stand (she calls him “King Midas’ idiot brother” because everything he touches turns to crap).