Interview: Michael Fassbender

After his sensational performance as IRA hunger striker Bobby Sands in Steve McQueen's Hunger, which shot him to fame at last year's Cannes, I was expecting to find him an emaciated shadow of his former self. For Hunger, he dropped two-and-a-half stone across ten weeks, his weight plummeting to a frail eight stone ten. So shocking was his appearance, it caused one doctor's receptionist to say upon seeing him: "That guy is really ill."

With Hunger winning him the Best Actor award at the British Independent Film Awards, Irish-raised Fassbender was suddenly white-hot – and when we meet this evidently has yet to cool. He's already been in Cannes for Andrea Arnold's searing Essex-set drama Fish Tank, which took a share of the Jury Prize. He then had to fly to New Orleans to work on a new comic book Western called Jonah Hex, before returning to help promote Quentin Tarantino's Second World War epic Inglourious Basterds. "I'm starting to realise which airlines I like and which ones I don't," he says.

It's a remarkable turnaround from what was an indifferent start to his acting career, landing minor roles in television shows such as Band Of Brothers and Murphy's Law. Not that he's beyond trotting out the usual actor platitudes. "It's all about whatever projects interest you," he says, diplomatically. "Mainly decisions come from working with directors I can learn from." To be fair, he's chosen wisely so far – from French auteur Franois Ozon, for his Edwardian fantasia Angel, to gritty British director Arnold, who has more than followed up on the promise of her debut Red Road with Fish Tank.

"Working with Andrea – she's a proper filmmaker," says Fassbender. "You have a film like Fish Tank, which is essentially a film that an audience can't just sit and allow it to entertain them. They have to get involved – and by the end of it, it's asking some pretty serious social and moral questions."

Fassbender plays Connor, the boyfriend of young single mother Joanne (Kierston Wareing) who endures a strained relationship with her two daughters. Unable to meet Arnold, as he was in South Africa when she was casting, he took the offer of the role after a brief phone conversation. "I'd said to my agent I didn't need to meet her," he says.

If this suggests that Fassbender works off his instincts, he's certainly not one to back down once he's on board. "It's all about just going for it and committing to it," he says. Hunger obviously took this, but his other films – such as the thriller Eden Lake, in which he and Kelly Reilly are terrorised by a bunch of hoodies, or Spartan scrap 300, in which he was buffed to the max – also required much physical commitment. Does he harbour some sick compulsion to put himself through the ringer on screen? "I don't know," he says, slowly. "I suppose there is some sort of masochistic streak in there. But I do like the physical side of the job. I think you can use your body to express a paragraph of dialogue."

Even Inglourious Basterds features another physically wince-inducing scene for Fassbender, who plays Archie Hicox, a former film critic and lieutenant in the British army. But to reveal all would give away one of the film's juicier moments. Hicox's character comes into contact with the Basterds of the title, a group of American-Jewish mercenaries (led by Brad Pitt's Lt Aldo Raine) who set about scalping as many Nazis as possible.

Fassbender – who starred in a stage version of Tarantino's Reservoir Dogs – swiftly moves to defend the director's fast and loose approach to real events. "We've seen so many World War II films, and I got a little bit bored of the same topics being treated in the same way. And I really thought it was refreshing – it took someone like Quentin Tarantino to rewrite history in his film and not to be confined by it."

With the film like a cinephile's view of the war, Fassbender's primary influence for Hicox was George Sanders, the British star who first played Simon Templar (aka The Saint) in a series of films in the 1940s. "I always had them playing in my trailer," he explains.

With Tarantino insisting the film be subtitled in parts, it also meant resurrecting his rusty German (his father is from there and Fassbender was born in Heidelberg). "I had a really good German teacher – and she put everything down on a Walkman for me, and I just walked around my apartment a lot with my headphones on," he says. With his mother from Larne, in Northern Ireland, it also meant shedding his soft Irish brogue, one developed courtesy of a childhood spent in Killarney, County Kerry – "a real beautiful part of the world" – where his family moved when he was two.

He's not related to the German filmmaker Rainer Werner Fassbinder, although "it depends what auditions I'm going for," he says. "He can become a great uncle of mine." He is, however, a distant relative of Irish freedom fighter Michael Collins (his mother being the man's great niece). Not that Fassbender has any need to namedrop. With Roman survival tale Centurion (with The Wire's Dominic West) in the can, and rumours of roles in the forthcoming big-screen version of The Sweeney and Sebastian Faulks' First World War bestseller Birdsong, he looks set to be the biggest actor out of Ireland since Colin Farrell.

For the moment, it's Jonah Hex that's occupying his thoughts. "I've always wanted to do a Western, and this character that I'm playing is really off the wall," he says. "A cross between 1970s Riddler and Clockwork Orange, with a really thick Kerry accent, in a western. So we'll see how it turns out. But again I'm working with some real heavyweights – Josh Brolin's playing Jonah Hex and John Malkovich is playing my boss. It's a real ride and I'm enjoying it at the moment."

Inglourious Basterds is released 21 August. Fish Tank is released on 11 September, www.inglouriousbasterds-movie.com

Interview: Michael Fassbender - Lean and mean