When I meet Jessie Buckley to talk about her new film, Wild Rose, she spends most of the interview excitedly leaning forward, right on the end of the sofa, almost as though she’s about to take off. Which, considering her career, seems appropriate. Directed by Tom Harper, with a script by Nicole Taylor (who wrote the BBC series Three Girls), the film wowed audiences at the Toronto international film festival. Variety called it: “A happy-sad drama of star-struck fever that lifts you up and sweeps you along”; the British Film Institute said: “Jessie Buckley was born to be a star.”

Fresh from her success as the troubled Moll in Michael Pearce’s psychological thriller Beast, which garnered Buckley, 29, a British independent film award for best newcomer and a Bafta rising star nomination, she plays Rose-Lynn Harlan, a brash young Glaswegian in white Stetson boots, whose dreams of becoming a Nashville country singer keep clashing with her real-life responsibilities as a single mother. Wild Rose has a recurring country music theme of “three chords and the truth”, and Buckley spends every onscreen moment acting and singing her guts out. Whether exploding into song while vacuuming in her job as a cleaner, clashing with her disapproving mother (Julie Walters), or tentatively (yearningly) stealing on to a soundstage at Nashville, she has you rooting for her in every frame. The result is a raw, Brit-country version of A Star Is Born, shot through with Full Monty-style underdog pathos, with a kickass performance at the centre. Rose-Lynn emerges so real, so alive, you not only sense her beating heart, you can almost smell her deodorant.

Jessie Buckley in Michael Pearce’s Beast. Photograph: Bac Films/Moviestore/Rex/Shutterstock

Today, sitting in a London hotel, Buckley is friendly and sparky from the off. Porcelain-pale, in modish dark denim, her red hair cropped into a bob, she chats away in her Irish accent, naturally articulate, her face animated as she speaks. Her career right now (awards, lead roles, transatlantic plaudits) seems a world away from her start as the nervous but game 18-year-old who came runner-up to Jodie Prenger in I’d Do Anything, the 2008 television search to find Nancy for the stage revival of Oliver!

Mostly, she is on tenterhooks about the release of Wild Rose. “It feels like you’re pregnant and you just hope that people are going to like your ginger baby,” she jokes. “But this is what you do it for – you’re proud of it. It’s a real people’s story, it’s of the people – it’s about an ordinary person doing something with their life.”

At the centre of the film is Rose-Lynn’s fractious relationship with her mother, affectingly played by Walters as basically the spoilsport, who reminds her daughter she’s got kids to look after. Neither Rose-Lynn’s father, nor her children’s father, feature – the other main character is Rose Lynn’s benevolent bohemian employer played by Sophie Okonedo. Certainly, it’s refreshing to see a film where childcare problems don’t just melt away. In Wild Rose, dreams spar with reality, and sometimes lose, or at least have to change shape. Could Buckley relate to that? “I don’t have any children, but I’m the eldest of five, so…” She narrows her eyes. “I suppose it’s like that for everybody [eventually] – when you have to be a grown up. There’s part of us, every morning, that might wake up and think: ‘I don’t want to bring my kids to school – I want to be feckless and free!’ But, in order to exist, and own your life, you have to take responsibility for the choices that you make.”

Buckley’s own singer/harpist/art teacher/music therapist mother has always been creative, as have all the family. Her father, a barman, writes poetry: “I think it’s in the Irish blood to have that musicality, creativeness, or, I don’t know, wildness,” says Buckley. “What I realised with my mum’s story is that, when you have a family, or when half of you kind of belongs to somebody else, you have to share worlds together… It’s easy to live alone in life. It’s harder, but more fruitful, to share.” Buckley loved working with Walters and Okonedo (“It’s like surfing with heavyweights”), and enjoyed the tight-knit Wild Rose set: “It’s rare to get that mesh of everyone experiencing something. It’s not always like that, sometimes you’re just wheeled on to perform.” It’s more businesslike, disciplined, you have to do what you’re asked to do. “Yes, but that’s fine – you still try to find that moment-to-moment creativity.” Then Buckley grins, adding: “I never completely do what I’m asked to do.”

Born in Killarney, County Kerry, Buckley attended a convent school she describes as “amazing”; she had friends, she says, but was unhappy. “Personally, I found school stressful. I grew up in that Celtic Tiger time. You had to be a doctor, lawyer, or whatever. Your happiness was based on materialism… I felt choked by it. At that age, you’re coming into your womanhood, you’re trying to have a sense of what you want from life. And, my God, I wanted to do music, to be in London, to be in the theatre… I realised that I had my own ideas about what I wanted. It was very hard at that point in my life – I suppose I was afraid of myself, and I was afraid of owning those feelings.” Buckley had therapy, and she thinks it’s important to be open about dark periods. “Sometimes it’s hard to be a person – we all meet different wolves within ourselves. What I want to explore in my work – as much as I want to explore it in myself – is a way of letting these things out, the foibles that we try to hide.” Is she still hard on herself, self-critical? “Oh yeah, with things that are important to me. I’m scared before certain jobs. Sometimes it can present itself in an actual panic attack, overwhelmed-ness, whatever.” Now the grin is rueful. “I’m not just going ‘Billy Big Guns’. It costs me because I love it so much.”

In Wild Rose, Rose-Lynn tries to get a break as a performer, something that echoes Buckley’s own experience. But she says the parallels didn’t occur to her when she was preparing for the role. “I didn’t look at it and go: ‘Oh, that’s my story.’” For Buckley, I’d Do Anything was an “escape tunnel”, especially as she was dejected, having just failed to get into drama school. I wonder if it’s harder, when you’re very young, to put setbacks into perspective? She nods emphatically: “Yeah, it’s like falling in love for the first time. It’s everything! When your love cracks for the first time, it’s like your world has exploded. But then you move on, and you have about five different boyfriends, and you realise: ‘My God, that was all a bit dramatic!’”

Jessie Buckley as Rose-Lynn Harlan in Tom Harper’s Wild Rose. Photograph: Entone Group

I watched I’d Do Anything and judges Andrew Lloyd Webber and Cameron Mackintosh seemed disappointed when Buckley didn’t win (in fact Mackintosh, whose production it was, looked positively gutted). Buckley says they continued to be supportive. “Cameron sent me to Rada to do a four-week Shakespeare course, for no reason. He just said: ‘Do you fancy doing that?’ And that was the first moment that world was exploded open to me. Andrew has always been a support, never asking anything of me, just: ‘Do you want to go for a cup of tea?’ When we meet we talk about different stories we’re looking to find, or whatever.” These were powerful people in her chosen industry – wasn’t she intimidated? Buckley says she was raised to take people as she found them. “I tried not to find it intimidating. You’re very raw, these are the kind of people you only heard about once upon a time, and all of a sudden they’re just standing in front of you. I suppose what’s amazing about creativity is that all these things can be dropped, and you’re just there, telling each other things.”

Buckley went on to do Stephen Sondheim’s A Little Night Music, and sang with a jazz group, but decided to go to Rada to study for three years. I’d wondered if she’d felt the need to legitimise herself in the wider acting world, but, in some ways, it sounds the opposite. “I was wanting to get off the track,” she says. “I always wanted to go and study. I came over when I was 17, and fast-tracked myself into growing up. I felt like there was more to explore, stuff I hadn’t fully realised about myself. And, you know, I wanted to go to the pub on a Friday evening and hang out with people my own age. I’d worked my arse off, but it was important for me to take a step back, just be my age, and surround myself with possibility.”

It paid off. Her CV includes Shakespeare productions (The Tempest; The Winter’s Tale), starring opposite Tom Hardy in Taboo, playing Marya Bolkonskaya in War and Peace (also directed by Harper), and of course, Beast. Buckley relished playing Moll, the off-kilter heroine. “Michael [Pearson] is so talented. When we were making it, it felt like there was an electricity… People said: ‘Were you tired shooting that?’ And I’m like: ‘No!’ Maybe, if the story had stayed how it was at the beginning of the film, but she was being reborn – Boadicea was coming out of her at the end!”

An unexpected outcome of Wild Rose was Buckley and Taylor (a Glaswegian and lifelong country fan) helping to co-write songs for the soundtrack (including the poignant Covered in Regret). Buckley has also continued rehearsing and gigging with her on-screen band, whose members include big folk-country names such as Neill MacColl (half-brother of Kirsty, son of Peggy Seeger), Aly Bain and Phil Cunningham. Taylor tells me that she couldn’t imagine Wild Rose without Buckley in it. “She’s so clever and eloquent, with such interesting insights about the script. And so unpretentious and a laugh… If she wasn’t so nice, it would be obnoxious how talented she is.” Taylor has seen all the Wild Rose shows, including supporting Kris Kristofferson, and says Buckley is the real deal: “People go mad for her. She’s got such stage presence, as well as the voice. This band are serious musicians – because Jessie’s properly got the musical chops, they were just: ‘Man, she’s amazing!’”

Jessie Buckley as Lorna Bow in the BBC drama Taboo. Photograph: Robert Viglasky/Scott Free Prods

While none of this was planned, Buckley is loving it, and doesn’t seem fazed by the idea of acting and music pulling her in different directions: “Maybe you have thoughts: ‘Oh no, I can’t allow myself to be that, because I’m this…’ But then, it’s like, fuck it,” she laughs. One of the songs she co-wrote is called That’s the View from Here (Famous Folk Are Weird). It’s from Rose-Lynn’s perspective, but how does Buckley cope with fame? She pulls a wry face: “With mass trepidation… I get scared. It’s just easy to get drunk on that world. It injects ego and all of a sudden, it can feel like the most important thing, but it’s not… I don’t know, I’m just figuring it out – how to be me in that world.” Buckley tries to be mainly “invisible” – hanging out with friends, cycling everywhere. She’s thrilled to receive awards, but sometimes finds industry events nerve-racking. “That’s the scariest part for me. I find the prep for those moments incredibly anxiety-inducing. I’m like, why can’t I just put on lipstick, and just go?” Usually I go to those things, and I shake. Then you see friends, and it becomes less scary. But you’ve got to take it with a pinch of salt. The moments that feel the most fulfilling and flattering are when I’m with amazing musicians having band practice, or something happens on set, and you feel that your whole self has been shattered and something new is coming out. That, for me, is when you want to lose yourself, not in the other situation.”

One dark side of fame is press intrusion, which Buckley got a taste of when her relationship ended with James Norton, her co-star in War and Peace. When I ask about this, it’s the only time Buckley visibly withdraws, saying haltingly: “I find it very uncomfortable. It’s my personal life.” On a more generalised tack, I wonder if having any kind of private life is difficult for someone in her situation? “I think in every aspect, you’re constantly trying to balance personal, private life, your work life, and everything else. It can become more heightened in this world, but you can also make choices.”

She feels the effects of #MeToo. “There definitely feels like a consciousness within our industry.” Later, she says: “I don’t think I’m ever going to be a beauty queen.” I’m sure many would disagree, though Buckley is just making a point, quite rightly, about not wanting to be objectified. “I’m not interested in that – I’m more interested in the character I’m playing. I think that’s such a wrong and stale message anyway – that your only value is what you look like … You either play to that, or you don’t. I think it comes from your sense of self. If I’m evaluating my happiness on what kind of mascara I’m putting on, then I’m probably missing out on a lot of other fulfilling experiences – ways of feeding my soul, or looking at the world.”

She also wants to be a good role model for her sisters. “I want them to feel like they can be whoever they want to be – just be your own self. If you nurture that, it’s the most beautiful, powerful thing that you can add to the world.”

Buckley has a veritable blizzard of projects coming up – roles in Charlie Kaufman’s I’m Thinking of Ending Things, Ironbark, a cold-war drama with Benedict Cumberbatch, The Voyage of Doctor Doolittle, with Rami Malek and Robert Downey Jnr, and Judy, the Judy Garland biopic, starring Renée Zellweger. “She’s extraordinary”, says Buckley of Zellweger. “She’d be doing a performance, a huge scene, and in between takes she’d just plonk herself down in the middle of all the extras and just natter to them like they were her aunts and uncles.” There’s also a Sky/HBO miniseries next month, Chernobyl created by Craig Mazin, starring Jared Harris and Emily Watson. Buckley found it moving to play a real-life character, whose husband was a firefighter at the disaster. “When you’re dealing with something like Chernobyl, people are still living with what happened… The woman I played, her story is one of blind love, loss, survival and grief. When I was preparing, looking at pictures of her and other people, it’s the grief that chokes you.”

Buckley’s career seems to have evolved into a sprawling mosaic – theatre, musicals, jazz, television, films, and now practically on the road with a country band. She isn’t sure she’s ever tried to plot a career path. “I just go with my gut instinct at that moment… and then suffer the consequences!” Yet she is not driven by a fear of being typecast: “I don’t really have a sense of getting stuck, because I’ll just probably derail myself.” Buckley agrees that, if she could have seen ahead as that downcast teenager not getting into drama school, she’d have been quite cheered by how things panned out. “In the moment, it did upset me getting knocked back, but that’s life – and thank God! I really believe, what’s meant to be doesn’t pass you by.”

Wild Rose is out in UK cinemas on 12 April. The soundtrack will be released on Island Records