There's a scene in Haywire, one of a trio of new movies starring man-of-the-hour Michael Fassbender, when he shares a pint of Guinness with Ewan McGregor.

It's the briefest of moments – and barely relevant to this all-action thriller about a rogue female CIA agent – but it almost feels like a changing of the guard. McGregor may be just six years older than the 34-year-old Irish-German actor, but their tastes and careers almost dovetail. Both are unconventional sex symbols, unafraid of screen nudity, with a penchant for provocative material. The only difference is that Fassbender is right now hotter than the sun's core.

He's far too humble to point this out, of course. "People have said that I remind them of Ewan, that we look similar," he offers, when we meet on an autumnal afternoon in London. In truth, there is some resemblance to the Scot – not least in the blue eyes and cocksure smile. It's our second encounter in six weeks, after he swung by the Venice Film Festival mid-way through a European motorbike trip with his father and an old school friend. Like McGregor, Fassbender loves bikes and he spent their days together "trying to pick his brain" over makes and models. "He's a much more competent rider than I am," he admits.

Part of Fassbender's reasoning behind his jaunt was to reconnect with family and friends after 20 months of flat-out work. Five films back to back – including playing Rochester in the recent Jane Eyre and the young Magneto in X-Men: First Class – have left him spent. But the A-list directors just keep on coming. Quentin Tarantino spotted him early, casting him as a British officer in his Second World War fantasy, Inglourious Basterds. Next month, he stars in David Cronenberg's A Dangerous Method, as Swiss psychiatrist Carl Jung to Viggo Mortensen's Sigmund Freud. And in the summer he'll play an android in Ridley Scott's Alien prequel, Prometheus.

If he's intimidated, it doesn't show: "You always are nervous. I always have a fear, anyway, going into any job, that I want to do the job right, or at least have some sort of quality of work there. There's a responsibility. You don't want to let such a great filmmaker as David Cronenberg down. You don't want to be the guy that messes up his story. So there's always the pressure. But then you've got to disrespect it all. There's a respect there but there should also be a certain element of disrespect. You've got to make decisions and you've got to do it. If you're worried about what people might say, then you'll just come unstuck."

For all his impressive work to date, it's this month's Shame that has caught the imagination. Already winning him Best Actor at Venice and the British Independent Film Awards, a Golden Globe nomination has put him up against such evergreen A-list players as Brad Pitt, George Clooney and Leonardo DiCaprio. And, without wishing to hex it, Bafta and Oscar nods seem assured. So will he "campaign", as Hollywood demands? "I don't know," he stammers. "All these things are very flattering and humbling."

While he is clearly reluctant to get caught up in the hype-machine, for once the plaudits are more than merited. Reuniting him with Steve McQueen, the director who cast Fassbender in his breakthrough role as the IRA prisoner Bobby Sands in 2008's Hunger, Shame is a searing examination of sexual addiction. Fassbender plays Brandon, a New York executive heading for a meltdown as he tries to satisfy his rapacious libido with prostitutes, pornography and one-night stands. Raw, honest, brave, it's the sort of performance you only see once in a generation (think De Niro in Taxi Driver for a similar New York-set study of loneliness).

Remarkably, it was even more taxing than Hunger, which saw Fassbender drop to a skeletal 57 kilos to play the hunger-striking Sands. "Mentally, it was a lot more distressing. The thing with Hunger, yes, I had to lose the weight, but I had a timetable over ten weeks that I just had to stick to. Like, 'OK, I have to eat 600 calories today' and you just go through it. It was like ticking the boxes. This was more- it's just pretty disturbing, the idea of what this character is about, the idea of relationships and us dealing with each other, and intimacy, and how for some people this is a difficult thing."

The way he talks, Shame clearly cost him something emotionally. Coming at the end of his cycle of back-to-back films, with much of it shot at night, he was barely sleeping and Brandon began to get under his skin. He recalls the scene where he discovers his sister Sissy (Carey Mulligan) has invited herself into his flat to stay. "I remember that was a particularly bad day. Just that I felt- I don't know- a bit vulnerable." Did he cry? "It's not even that simple. Close to it, if not. Just a sense of being a little bit lost in something. I don't really want to get into it." It's one of the rare times the candid Fassbender closes off. "I always think it's really boring when actors talk about that."

Despite playing Jung for Cronenberg, in a story that elegantly dissects his relationship with Freud at the birth of psychoanalysis, Fassbender is not in therapy nor is he addicted to self-help books. He prefers the old-fashioned route: thrashing out his problems over a pint.

"I have an open relationship with my friends," he says, claiming he isn't afraid to appear "vulnerable" in front of them. "I try not to be affected by insecurities. These are things that we have within us all, and we all suffer from them."

While Freud might have a field day with the sexually deviant characters Fassbender is currently playing (as Jung, he gets to spank Keira Knightley's sexually repressed patient), he'd be mystified by the solid, healthy relationship he seems to have with his parents. Born in Heidelberg to an Irish mother and German father, he spent much of his childhood in Ireland's County Kerry, where his parents ran a restaurant. "If you've got a family business, you're all trying to make it work together," he reasons. "So I would work with them in the restaurant, and a different relationship formed from that. I'm very blessed and very lucky to have that."

Before you ask, no, he's not related to the iconic German filmmaker Rainer Werner Fassbender. He is, however, a distant relative of Irish freedom fighter Michael Collins (his mother is his great niece) and even played him in a stage production at the 2006 Edinburgh Fringe. However, growing up, he yearned to rock. "I wanted to be a guitar player, but I wasn't good enough." Then he met drama teacher Donal Courtney.

Once the acting bug bit, after a year's theatre course in Cork, Courtney suggested he "study properly", so he moved to London, where he still lives, and enrolled at the Drama Centre. Upon graduating, he found immediate employment in a production of Chekhov's The Three Sisters, while working in a warehouse to make ends meet. In 2001, he thought his money worries were over for good when he landed a role on the Second World War TV drama, Band Of Brothers. But then he didn't land another part for 12 months and, even then, had to make do with bit parts on TV shows like Murphy's Law.

It wasn't until he won a key role in Zack Snyder's 2006 Spartan epic 300 that his career truly took off, which may account for his humility. "I don't read interviews that I've done. I don't read about myself. I try to steer away from all of that. I think that keeps me - living in ignorance. Also, my friends and my family, they're not going to listen to me talking s***. And I'm just really happy with the work I've been allowed to do. And, on the other side, people don't really recognise me. Who knows? Things might change, but I just try to keep everything simple really."

The only thing that seems to have suffered is his love life. Aside from briefly being connected to his X-Men co-star Zoë Kravitz, the 22 year-old daughter of singer Lenny, Fassbender has remained resolutely single, and marriage seems a long way off. "I always admire people that are married and can work a marriage in a business like this, because it is such a gypsy lifestyle. You get up, you go somewhere else, you're in another country, another hotel room. And you don't really see the person. So it's very difficult, I think." For now, he's all about the job – what he calls his "number one passion". And there's no shame in that.

Shame opens on January 13, Haywire on January 20, A Dangerous Method on February 10 and Prometheus on June 1.