TORONTO - Saoirse Ronan can understand the scene in “Brooklyn” where the middle-aged mother cannot bear to watch as her younger daughter sails off to America.

The 21-year-old actress had FaceTimed her mum that very morning, she told a handful of writers at the Toronto International Film Festival in mid-September.

“She was starting to cry as I was getting off. She was like, ‘Just do great!’ and she got off the phone.”

The actress, born in the United States and reared in Ireland, has been doing great for years.

Nominated at age 13 for a supporting Oscar for “Atonement,” she should be back on the awards circuit for her leading role in “Brooklyn.” Next year, she will make her Broadway debut in “The Crucible,” at the invitation of Scott Rudin, who produced “The Grand Budapest Hotel,” in which she appeared. The revival, which starts previews Feb. 29 and opens April 7, also is expected to star Ben Whishaw, Sophie Okonedo and Ciaran Hinds.

“Brooklyn” casts Ronan as Eilis Lacey, an Irish immigrant navigating her way through 1950s Brooklyn. When she finds romance and employment on both sides of the Atlantic, she has to decide which path and partner to take.

Emory Cohen and Domhnall Gleeson portray the suitors, Jim Broadbent is a kindly priest, and Julie Waters is the landlady of her Brooklyn boardinghouse. John Crowley directs the film, based on Colm Toibin’s novel, adapted by Nick Hornby.

Eilis’ journey meshed perfectly with Ronan’s desire to graduate to adult roles (this one comes with a PG-13 rating).

“I think I had never played kid roles and I had never been in kid films, so I had always thought about myself as just an actor, really. But when I got to about 18, 19, up until now, really, it was tricky to showcase that you were ready to move on to that next step of taking on roles that were just a little bit more mature and where you were personally, and so ‘Brooklyn’ came along at the right time for me.”

Eilis leaves Ireland, moves into the boardinghouse with other unmarried women, starts a job as a saleswoman at a classy department store and meets an Italian-American man at a dance. When a family tragedy pulls her back to Ireland, she spends time with another young man and is pressed into service in an office there.

“What’s rather interesting and true to life about the story is that it suggests that the heart is capable of being loyal to more than one person. It’s a difficult thing to achieve as a storyteller,” director Crowley said.

He has to ask the audience to spend the better part of an hour believing in her story, her loneliness and then her happiness at finding one person in the world for herself and falling in love.

“And then park it, while you develop another love affair without making an audience want to blow the whistle and go, uh, ‘Foul,’” he said. “And believably see that what those two men represent are two very different lives for her and two very different versions of herself.”

When Ronan, blond hair just past her shoulders and fashionably clad in a short-sleeve black dress with spiky heeled booties, made the rounds of interview rooms at the Fairmont Royal York in Toronto, talk also turned to America, Ireland and accents.

“Losing my Irish accent? Never. I’ll never lose my Irish accent. I always want to sound like a leprechaun.”

She is fascinated by accents.

“It’s always the first thing I think about, the voice of a character really defines who that person is. And I love that.”

It’s almost like a musical instrument when used in the right way.

As for Ireland, that is where she anticipates raising her children down the road.

“That’s where I’ll settle down or whatever, I reckon. That could change but I don’t think it will. And New York is a really huge part of me. That’s where I was born. I lived there until I was 3, and it very much made my parents into the people that they are.”

Her fiercely independent mother, whom she’s “basically a clone of,” had been adamant about giving birth in the States, to spare her child the legal tangles and wrangles she and her husband faced in obtaining visas after living in America illegally.

They returned to Ireland with their daughter, and when she started school there, she was considered an outsider.

“I remember one of the kids saying to me on my first day, ‘You’re from America, you’re weird,’ and no one would talk to me for my first few days at school when I was 5.”

That was 16 years, two dozen movies and TV series and roughly 52 nominations or awards ago.

“The fact I can call myself someone who comes from both places is a real gift they gave me. They’re both home in different ways. I think Ireland, that’s my childhood, that’s where I went to school, that’s where my family is. That’s very much my roots, but New York, it’s almost like these two different personalities that I guess make up who I am.”

She is moving to New York next year for the play and says, “I’ll probably stay there ‘cause I love it so much. It’s that chapter in my life that was always waiting to happen. … I moved away to London when I was 19 because that was a more sensible first step, but it was always going to result in New York.”

Ronan kept a small reminder of her time in “Brooklyn,” including what she jokingly calls “that very glamorous scene where she’s on the ship and there’s a bucket involved.” It serves a couple of unwelcome purposes on a ship navigating rough seas.

“We were on this massive gimbal,” being rocked and rolled on the set in Ireland by long-haired guys in Metallica T-shirts. “I stole a towel, a tiny one, just a little one,” from her character’s shipboard cabin. “I still have it. I brought it to my flat when I was done, so it’s like my little reminder of ‘Brooklyn.’”