Mila Kunis: The other Black Swan finds her feet

Ukraine-born Mila Kunis missed out on a Golden Globe for her role as Natalie Portman's rival in their new film but is still on a high.

There may come a time when Mila Kunis looks back on Black Swan as a moment of metamorphosis. Already Darren Aronofsky's sublime psychosexual thriller set in the ballet world has seen the 27-year-old bestowed with the Marcello Mastroianni Award for Best Young Actor or Actress at the Venice Film Festival. Now, though she lost out to The Fighter's Melissa Leo, an Oscar nomination seems like a certainty. Of course, she won't allow herself to think about this just yet. "I wouldn't know what to do. I am so not a part of this world," she says. "For me to be nominated in any awards show is such a shock. I come from such a small town in the Ukraine!"

Born Milena Markivna Kunis, she grew up in Chernivtsi, in the southwest of the country. Raised with her older brother, Michael, by her mother, Elvira, a physics teacher, and her father Mark, a mechanical engineer, her family applied to move to the States at the tail end of the communist era. "My parents wanted my brother and I to have a future," she says, her high-speed West Coast chatter devoid of any traces of an East European accent. When they arrived in the US, the seven-year-old Kunis didn't speak any English. "I didn't study it. I didn't have a book. I didn't learn it. I just surrounded myself with it. Right now, if you did that to me, I wouldn't know what to do with myself."

While her father enrolled her in an acting class when she was nine, she started acting professionally three years later. Though playing the young version of Angelina Jolie's drug-addicted model in the Golden Globe-winning Gia early on, her success so far has come largely in television (a regular role in sitcom That '70s Show and voicing Meg in Family Guy). Her films to date – like straight-to-video sequel American Psycho II: All American Girl – are hardly what you might call Academy-friendly. "I stand by every movie that I did," she says, defiantly. "I don't regret any decision I made. Whatever I did, I always grew, whether as an actress or a person. And in my experience, you never know what movie is going to open what door for you. It's always the ones you least expect."

In the case of Black Swan, it was Forgetting Sarah Marshall, the 2008 comedy in which Kunis played the sweet-natured hotel clerk. Compared to her Black Swan character Lily, a sexually confident ballerina, the role couldn't be more different. Nevertheless, it was a performance that convinced Aronofsky. "She just leapt off the screen," he says. "She was just so sexy, beautiful, charming and free." Dressed today in a charcoal skirt, sleeveless white top and a pair of black high heels that elevate her 5ft 3in frame – completing the Lily-like look with black nail polish – it's not hard to see what he means. Long brown hair, olive skin and magnetic oval-shaped hazel eyes lend her a beguiling minx-like quality.

So taken with Kunis was Aronofsky, he gave her the role without an audition. "Black Swan is the first time where a brilliant movie was handed to me," she says. As Kunis puts it, they "chit-chatted" on iChat three times, with the director casually asking her if she was "ready to do this" during their third conversation. Admittedly, it helped that Kunis was good friends with Black Swan's star Natalie Portman, who plays Nina, the virginal New York ballerina at the core of the film. Kunis met Portman seven years ago through mutual friends. But it was on a Sunday morning trip to a flea market in LA, where Kunis lives, that she first heard about Black Swan.

Portman told her she was following their shopping expedition with a ballet lesson. Kunis replied by telling her that she once broke all of her toes dancing. "I have two left feet," laughs Kunis, who – as a video-game devotee – is something of a tomboy. "I have no rhythm. I had never considered myself a dancer, and I probably never will." Yet in spite of this, Portman went straight to Aronofsky to recommend her, only to discover she was already on his radar. If this serendipity is reward for years of little-seen television and film roles, Kunis more than paid for it. "By far" the most physically demanding role of her career, she had to transform herself into a ballerina. Dropping 20lbs from her already slim physique, she went through seven months of "excruciating" training to learn the discipline.

Working four hours a day, seven days a week, she took only one day off – for her birthday. All she had to look forward to every night was a hot bath, filled with Epsom salts, and an accompanying glass of wine. And she didn't escape injury – dislocating her shoulder two weeks before production began and tearing her calf ligament during rehearsals. She also now boasts two scars on her back from where she was lifted for six hours a day. But Kunis says she refused to feel sorry for herself and her war wounds. "An opportunity like this very rarely comes about. So if you complain, you kind of feel like a baby, so you choose not to."

Compared to Portman, who went through a similar transformation, Kunis has far less screen time actually dancing. Yet her presence is vital in a film that deals with Nina's mental disintegration as she takes on the gruelling dual role of the Swan Queen in a production of Swan Lake. Unable to find it within herself to dance the part of the Black Swan, Nina becomes increasingly paranoid that Kunis's free-spirited Lily may snatch the part from her. The problem for Kunis is that Lily is viewed through the eyes of Nina, who increasingly sees her as a doppelgänger. "The character was so odd to interpret because you could take her any which way," says Kunis, "and no one way is going to be wrong."

A film about obsession more than madness ("anyone can spiral downwards, if they want to pursue perfection," says Kunis), it's also hooked on Nina's sexual awakening. One particularly crucial scene, as Nina and Lily wind up in bed after a reconciliatory night out, sees Nina experience her first orgasm, meaning Kunis and Portman had to set aside their friendship and share an awkwardly intimate moment. "Anytime you do a scene that you have to have sex on camera is just uncomfortable," shrugs Kunis. "Male, female, makes no difference. But if you're comfortable with your partner in the scene, and you know them, it makes things a lot easier."

Still, it seems entirely apt that a film about transformation is set to change Kunis's career – though she seems strangely cynical on this topic. "Ask me in a year and I'll tell you," she says. Much of her recent film work has been in comedy – Date Night, Forgetting Sarah Marshall, Mike Judge's Extract and her forthcoming movie, Friends with Benefits, in which she stars opposite Justin Timberlake in a story about two friends "who like to have sex". There's even talk that she will be joining the cast of Ted, written and directed by Seth MacFarlane, the creator of Family Guy, in which she'll play the girlfriend of a guy whose teddy bear has come to life.

Maybe Black Swan will be an anomaly in a comedic career. After all, her more dramatic outings – video-game adaptation Max Payne, the Hughes' Brothers' apocalyptic tale The Book of Eli – have left much to be desired. But Kunis is happy to take it step-by-step. "In this industry, it's not like a game of chess, it's more like a game of checkers, as I like to say. So you can't think four or five steps ahead, because it's impossible. I'm in a position where you don't have to work for the sake of working. I'm very lucky in a sense. So I can sit back and wait for a project that I respond to and that I want to do. So it's pretty much all I do. It's just finding a project that you're drawn to."

It helps that throughout her rise she's had someone on hand to advise her of the pitfalls of a Hollywood career. Since 2002, she's been dating Macaulay Culkin – though recent reports have confirmed that the couple has just split, which may explain why the Home Alone star has not graced one of the red carpet premieres for Black Swan with Kunis. In the past, she's called him "a steady rock", noting they "grew up together". Yet with her career on the rise, and his having largely stalled, perhaps it's no surprise that they've outgrown each other. For the moment, Kunis has more immediate concerns – like riding out the most important awards season of her life.

'Black Swan' opens tomorrow