In her graceful portrayal of Felicia Montealegre Bernstein in “Maestro” — opposite director Bradley Cooper — Carey Mulligan turns what might have been Cooper’s solo performance into a duet. Born in Costa Rica and raised in Chile, Felicia is an up-and-coming actor in New York City when she goes to a party and meets Lenny, an ambitious conductor and composer. After they marry in 1951, she has three children with her lightning bolt of a husband, who is sexually oriented more toward men.

But she’s not pathetic; Felicia is Lenny’s partner in every sense of the word. In a way, Felicia is the consummate Mulligan performance: Her simmering interiority meshes with Cooper’s magnetism, which is Mulligan’s own form of conducting.

Mulligan first began talking to Cooper about “Maestro” in the summer of 2018, after he came to see her in the Off Broadway play “Girls & Boys.” Cooper had completed “A Star Is Born,” his directorial debut, but it wasn’t out yet — and he was planning his next film. She read the screenplay for “Maestro,” written by Cooper and “Spotlight” Oscar winner Josh Singer, and it felt to Mulligan “like the kind of role that I had had the privilege to play onstage, but not yet really on-screen.” She says, “It felt epic in a way — the breadth of her life and the journey she went on just felt so rich. I was obviously just desperate to start playing her.”

In her two Oscar-nominated performances, Mulligan has revealed her range, playing an Oxford-bound 1960s teenager whose life is nearly derailed by a charming predator in 2009’s “An Education,” and a woman fueled by rage after the rape of her best friend in 2020’s “Promising Young Woman.” In both films, Mulligan’s acting was precisely calibrated and layered, skills she’s also applied to her roles in “The Great Gatsby,” “Shame,” “Drive” — and now “Maestro.”

As an activist, Mulligan’s deep-rooted empathy makes her an obvious Power of Women honoree for her work with War Child UK, an international organization that protects children in conflict zones. She began working with the organization in 2014, after its CEO, Rob Williams, invited her to the Democratic Republic of Congo, where Mulligan saw the transformational work they were doing with children who’d been through terrible trauma.

She’s been a global ambassador for War Child ever since, and her husband, the musician Marcus Mumford, soon followed suit. Between them, they try to take a trip with War Child once a year. Mulligan has visited Iraq, Ukraine and Jordan.

She doesn’t go just to bear witness. In Ukraine last year, she did art therapy with Roma refugees. In Jordan, she met with a group of girls ages 10 to 13, who all told her what they wanted to be when they grew up. One girl said she wanted to be a judge, another a policewoman. Then a “really shy girl,” Mulligan says, was called upon. “She stepped forward and said, ‘I want to be an architect, so that if my house is destroyed, I’ll know how to rebuild it myself.’ It just floored us that it was her mindset that she needed to think like that — but that she had also the ambition to think like that.”

Mulligan credits War Child’s educational program for instilling the girls with confidence. “They really had this sense of ‘I can have a future for myself, and I can build it myself.’”

Mulligan and Mumford also throw an annual fundraiser for War Child — this December will mark their 10th — which helps her channel the helplessness of watching the news and feeling “Oh, my God, there’s nothing that we can do,” she says.

During the actors strike, Mulligan spent most of the time with her family in England. “Maestro,” meanwhile, premiered at the Venice Film Festival, and is scheduled for a limited theatrical release on Nov. 22 before it begins streaming on Netflix on Dec. 20. Under normal circumstances, Mulligan would have been discussing the movie for months already, but because of the strike, “this is the first time I’m talking about it!” she says.

What made you want to play Felicia?

I obviously have known Bradley for a long time. He had come to see lots of theater I’d done in the past, and we knew each other largely through that. He’d come to see “Skylight” when I did that with Bill Nighy on Broadway. He also saw it in London. And we’d kind of bumped into each other along the way.

And I’ve been such a huge admirer of his work as an actor, and also as a director. I loved “A Star Is Born” — it absolutely ruined me.

After you took the part, what kinds of conversations did the two of you have about the film and about who Felicia was?

It was clear from the beginning that he was working with Felicia and Lenny’s children really closely, and that this was a story that was really coming from them, and from Jamie Bernstein’s book. Her book is just so brilliantly written — you really feel like you’re sitting at a dinner table at one of their amazing dinners and fabulous parties.

It’s funny — we always refer to them as being “the kids,” even though they’re grown people. But whenever we spent time with the kids, you sort of wish you could be in that family for a minute. It was just such a fun, eccentric, exciting, beautiful and very, very close environment to grow up in. We had these incredible tapes and interviews of Felicia and Lenny talking.

And there were so many fascinating things about her as a character to me — the sense of a bit of a life unlived. There was an unknown element to what she could have been had she not met Lenny — there’s a sort of “Sliding Doors” thing going on with her. She came to New York with this passion and desire to act, and was following that path really successfully. Then she met him, and they became each other’s world. But that obviously put her career on the back burner.

When you were talking to the kids, did they give you anything of hers that helped you unlock Felicia as a character?

If you see the film, smoking was a real hobby for both of them. A passionate hobby. They gave me her lighter, which is this beautiful gold-plated lighter with her name engraved on it. So I had that before we started shooting, and I used it in the part of the film where she would have had it, which is the ’50s onwards.

How else did you research her life?

I also went to Santiago and met her family. I spent a couple of days down there chatting with them and getting a sense of her. I saw some of her original artwork. I started by sitting with them making notes in a notebook, and by about five minutes in I was like, “Well, this is just pointless — I just need to sit here and absorb this.” Because the energy was just so incredible.

As I got to the airport to leave, I found out I had COVID, so I had to stay on. And, actually, I spent the rest of the time that I was there painting and re-creating Felicia’s paintings — and I’m not a painter!

I was going to say, I didn’t know you were a painter.

I’m not, and I hadn’t painted probably since I was, like, 5 years old. Three months before that, I’d started doing painting lessons, because painting was a big part of Felicia’s life. There were originally scenes in the movie where she was painting, and I thought, “I don’t want to look like I have no idea what I’m doing,” so I started going to painting classes, and I absolutely loved it.

When I got stuck in my hotel room in Chile, I said to Netflix, “I can’t come back, I’ve got COVID.” And they said, “Well, what can we send you?” I said, “I just need a canvas and some paints!” 

I love how the movie doesn’t explain their relationship — it’s a given that they love each other, and there’s no dramatic moment when we see she’s discovered that he’s more oriented toward men. What did you think of that?

I hope when you watch it you see that there is just a complete, whole connection between the two of them. There’s an inevitability to their relationship, and the minute they meet, there’s just something that has drawn them together, irrevocably, and that’s it.

There’s a letter in his book of letters where she writes, “I know that you are a homosexual,” but that she’s comfortable with it, and she doesn’t care, basically. She commits herself to him with the full knowledge. It felt to me that the betrayal for her — and the sense of loss that she experiences — isn’t to do with his physical relationships with other people. She was his everything; she was his muse, his inspiration, his closest confidant, his best friend, his lover. I think it was the fact that he started looking to somebody else for the comfort and reassurance and support that he needed in his life. And that was what, ultimately, she found too difficult.

When she says, “I know exactly who you are,” she really does. That part of the relationship — there’s no surprises for her there. They had been this tight, tight, unbreakable unit, and that started to sort of fray. And that was what she couldn’t deal with.

There are so many scenes when Felicia is watching Lenny. How do you project her interiority?

We really rehearsed it like a play. We had so much prep. We also spent a week together doing a specific workshop just on our two characters — just Bradley and I digging into who Lenny and Felicia were, and how that connected to us.

Bradley had done mammoth amounts of research and preparation in all aspects, because he needed to direct the film. I’ve never seen anyone prep for a character the way that he prepped for Lenny. It was astonishing. He was ringing me up in the full dialect a full year before we even got to New York. I mean, it was unbelievable. By the time we were shooting it, it just didn’t feel like we had to think very much. And I think it was the sort of not having to think about it that made it very easy to just respond to stuff.

I will get on set sometimes and just freak out, because I feel self-conscious, or I feel like I’m not ready. I never felt like that on this set. I always felt like I couldn’t fail. Bradley made it feel like you couldn’t, and that was the environment that everyone walked into.

Felicia knows who Lenny is, but she’s not always happy about it, as we see as the story moves along. How did you project her strength?

It was very much in what she said about herself. She said in one of her interviews, “I either do it completely or not at all. If I find myself feeling resentful, I excuse myself completely.” She wasn’t in the market for being someone who would be a victim, ever. She didn’t want to view herself like that, and she wouldn’t allow herself to be like that.

You mentioned that when you read the script, it felt like a role that you’d played onstage, but not on film. What was it you saw in Felicia that you had never done before?

This might sound like sort of therapy now, but I didn’t go to drama school. I didn’t train. I just started acting when I was 18 and got into it. But there was a part of me that always felt like I wasn’t a proper actor. There was a part of me as an actor that always felt like, “Well, I’m never going to be one of those actors that keeps their dialect in between takes.” There was a part of me that was slightly held back, or maybe nervous of completely committing to something.

But that was what Bradley asked, basically, at the beginning of the process. He was like, “If you’re going to do this, you just have to fully, fully do it.” When he said that, I was like, “OK, I’m going to absolutely do it all.” I’m going to do all the research. I’m going to do all the dialect stuff. I’m going to do everything, so that when I get on set, I am 100% able to just feel like I’m onstage and have that sense of “I don’t remember what happened.”

The great nights for me when I’m onstage are when I walk off and I’m like, “I have no idea what just happened!” Maybe that’s not the best thing for the audience, by the way? It could be that I just went onstage and did something massively self-indulgent.

But I love that feeling of “I can’t remember what that was!” And that was my experience on this. I felt that freedom that I had had onstage. The awareness of a film set, or of a camera, was gone. 

Styling: Olivia Buckingham; Makeup: Emma White Turle/The Wall Group; Hair: Bjorn Krischker/The Wall Group/ORIBE; Production: Joel Gilgallon/Joon Represents; Location: Bovey Castle Hotel, Dartmoor National Park, Devon, England, ; Look 1 (Black and white stripes): Full look: Valentino; Jewelry: Stephen Webster; Look 2 (Green dress): Dress: Victoria Beckham; Rings: Stephen Webster; Look 3 (Plaid coat look) Full look: Emilia Wickstead