Iwan Rheon is an Olivier-award-winning actor with an understated charm and a penchant for playing troubled teens. He also happens to be the star of John Osborne’s The Devil Inside Him, one of the biggest coups for Welsh theatre in years. He talks to Ben Bryant about mod, misfits, and his life on the stage so far.

Iwan Rheon is outside, smoking. The 24-year-old, who won an Olivier award this year for his startling performance in Spring Awakening, has just finished the day’s rehearsal for The Devil Inside Him. Deemed lost until it turned up in the archives of the Lord Chamberlain last year, the John Osborne play is showing at the New Theatre for the first time in 60 years. Naturally, its debut is a real coup for National Theatre Wales. By turns funny and tragic, it tells the story of a teenage outsider in a village in West Wales, and seems perfect for Iwan, who’s played troubled adolescents throughout his career.

In person Iwan is understated, modest and a little self-conscious, fiddling with his shoelaces and scratching at his stubble. His hair falls in an unkempt fringe across his forehead. With his desert boots and button-down shirt, he’s unmistakably mod – “I’m in a mod band, yes,” he later admits sheepishly – and although he’s 24, he seems younger.

Iwan was born in Carmarthen in 1985, and has lived in Cardiff since the age of five, when his father came here to take a new job. Neither of his parents’ families have a history in the arts. His father an accountant and his mother a social worker, he was state-educated at Ysgol Gyfun Gymraeg Glantaf in Llandaff North, and it was here that he was first exposed to the stage, participating in youth theatre and a lot of work with the National Eisteddfod.

The appeal of the stage was simple, he says: “It’s something you’re on your feet doing it. It’s creative. I’m dyslexic, so sitting down and writing in lessons wasn’t ideal for me. It was quite a nice release for me to do something more vocational, which was great for me at the time.”

Although he’s curiously withdrawn – shy, even – there’s a roguish quality to Iwan that makes it tempting to draw lines between him and the characters he plays. He’s quick, however, to emphasise how normal his school life was: “I wasn’t, you know, Mr Popular,” he says, visibly cringing at the thought. “I was somewhere in the middle ground. I was quite alternative, the things I liked to do. Skateboarding, at the time. Playing in a band as opposed to playing in the rugby team. You know, that kind of thing.”

Did he possess any of the outsider mentality that’s so apparent in the characters he plays?

“I think everybody knows how it feels to be in those situations where you feel insecure or whatever,” he shrugs.

His first break came with Welsh language soap Pobol y Cwm. His successful audition for the part made him seriously consider acting for the first time, he says: “When you get to sixth form you think, ‘Right, what do you want to do with your life?’ And you think, ‘Ooh, I don’t know, marine biology?’ – and all those sorts of things. But it came down to – I think it must have been a careers meeting or something – and I just went, I wouldn’t mind being an actor”

For somebody who almost fell into acting, Iwan has done remarkably well. Earning a place in the London Academy of Music and Drama, he moved away from Cardiff with his parents’ blessing and, just a year after graduating, he landed a place on Spring Awakening. The play took home four awards including Best Musical at this year’s Olivier Awards, and Iwan himself was awarded Best Performance In A Supporting Role In A Musical for his role as Moritz Steifel. Cool and subdued before, he’s a different person when he’s talking about winning the award: “I’ve never felt anything like it,” he says. “Going from being heavily nervous to being completely elated and on cloud nine is an amazing feeling.”

He’s just as enthusiastic about Spring Awakening. “I think it’s great for the show to be recognised, because it finished before it should,” he says. “It got great reviews, but it should have got more recognition from the fact that the show itself won the Olivier as well.”

Iwan’s much better at talking about plays than himself. Sitting a little straighter in his chair, we talk a little about The Devil Inside Him. It’s obvious that Iwan’s developed a connection with his character Huw Prosser, a disaffected poet growing up in a conservative Welsh village.

“He’s quite different,” he says. “He wants to go out into the hills and write poetry, and follow impulses that maybe should be crushed. In that way he becomes an outsider, and everyone sort of pushes him and picks on him, and thinks he’s weird and daft and sick.”

“He’s an outsider,” he continues. “He’s very poetic and he sees the world in a different way. He has a love for words.”

Iwan’s zeal for the theatre makes it easier to understand his hesitance at relating himself to the characters he plays, for fear of being typecast, but it’s clear that this dreamer has more in common with Huw than just their homeland. Is it that love of words that chimes with Iwan?

“I write songs and stuff, so in a slightly different way to him, but yeah. He wants to just be outside and be free. He wants to be free.” – and Iwan’s almost lost at this point, his green eyes flicking to some indeterminate point over my shoulder – “He’s trying to understand the society and be free. And I think that’s something I can identify with.”

The Devil Inside Him, New Theatre, Cardiff, Thurs 6-Sat 15 May.

Tickets: from £7.50 (cheaper if you’re 16-25). Info: 029 2087 8889 / www.newtheatrecardiff.co.uk.