As wild child Fiona Gallagher on “Shameless,” which returns for its fifth season this month, Emmy Rossum has shown off some serious comedic chops along with dramatic flair. But it was her singing voice that would land her a role in “Songcatcher,” a first mention in Variety — and take her to the Sundance Film Festival.

Did you see this review when it ran?

I remember how excited I was to see my name in Variety. I remember the picture, too, because I don’t remember it having been taken. It was one of those candid moments when I was methoding. I always really liked it because it was taken at a moment when I wasn’t trying to look like anything.

How did you get the part?

I was singing in the Metropolitan Opera children’s chorus, from age 7 to 13. The producers making “Songcatcher” came to the opera to audition young singers. I had just lost my baby teeth — I was a late teeth loser. I had gotten this “flipper,” a retainer with fake teeth attached. I showed it to the director, who thought I looked like such a hick. To this day, I think that’s part of the reason why I got the role — because I was missing teeth.

Did you enjoy making the film?

It was made in the backwoods of North Carolina. We would sit around on porches until nightfall in the middle of the woods. I was this girl from Manhattan — I’d never seen that kind of life. It was my first experience really understanding what it takes to become a different person for a role. I was hooked.

Is that when you decided you wanted to become an actress?

The biggest compliment I got (when we went to Sundance) was that people were surprised that I wasn’t from Appalachia, that I was a New York City girl. The idea that got me so excited about being an actor was being able to transform into someone else and be believable.

Who were your mentors?

I had a singing teacher at the opera. Strict would be an understatement. She was all about the technique, the singing and the professionalism with which you showed up to work. That kind of work ethic has been so helpful now that I work with (showrunner) John Wells, who doesn’t allow sides or scripts on set. You need to show up knowing every word before you set foot onstage. That kind of rigorous training that you get in a classical music background really trained my brain to work in that way.

What do you wish you had told your younger self?

Breathe more. I feel like I held my breath for years just trying to be perfect. But at a certain point when you’re in the moment, you can’t be thinking about perfection. Because the greatest moments come from mistakes. If you’re present, whatever comes out, that’s the right option.

What do you consider your big break?

“Songcatcher,” for sure, and “Mystic River.” It was my first studio film. Speaking of not breathing! I hardly remember the experience because I was so awe of everyone I was on set with. I really felt almost spiritual because you’re around so many great actors you’ve watched for so many years. When you’re in a scene with Tim Robbins and Sean Penn, it’s hard to breathe.

What have you learned from playing Fiona?

That women don’t have to be glamorous to be considered sexy. I think that was so eye-opening for me. For someone who doesn’t wear makeup or fancy clothes, I think that was for me really liberating in a way. You can raw. You can be aggressive. You can be vulnerable. And you can be sexy.