Will Hollywood change Robert Sheehan? Not likely. The tousle- haired thespian has been living in Tinseltown at “as fixed an abode as an actor can manage” but still sounds unaffected enough to have just stepped off the last bus from his native Portlaoise. That’s probably just as well. “I travel pretty light,” he says. “Unencumbered, you know? But that’s because poor old mum and dad have an attic full of my stuff back at home.”

At 27, Robert Michael Sheehan has enough stage and screen credits to be considered a veteran. His extraordinary career stretches back to 2003 when he took a bow in Aisling Walsh's Song for a Raggy Boy. When he sees his younger self on screen, can he remember what he was doing? "No, I look back on stuff all the time and think 'I couldn't do that now' or I don't recognise it."

He broke into movies without any formal training, but he did try life on the other side of the camera at the Galway-Mayo Institute of Technology. He left after a year having landed roles in the Irish movies Summer of the Flying Saucer and Cherrybomb. A stint in Channel 4's noir trilogy, Red Riding, sealed his fate.

“It was a very weighty project,” recalls Sheehan. “It felt like a step up, especially coming after those other roles in quick succession.”

He subsequently made a splash at the Old Vic in John Crowley's production of The Playboy of the Western World and as a regular in three seasons of RTÉ's Love/Hate. But his Bafta-winning turn as Nathan Young in E4's Misfits remains the role that changed everything. It is something he discussed with Dev Patel, his co-star in the new movie The Road Within.

"Dev had the same thing with Slumdog Millionaire that I had with Misfits," says Robert. "They are great roles but they're so defining in your career. It's the job that's really beneficial, it's the one that everybody loves – and suddenly you're left with the challenge of putting it behind you."

That's a sensation that Robert Patrick, another Road Within player, knows all too well: "He went through a difficult sort of phase after Terminator 2 when he couldn't get seen for roles. Even now, when I was saying to my mates at home, Robert Patrick is playing my dad in this movie, they didn't know who I was talking about until I said T-1000. And then they were impressed."

The Road Within sees a germaphobe (Dev Patel), an anorexic (Zoe Kravitz) and a guy with Tourette's syndrome (Sheehan) on a journey toward the ocean. The latter has just lost his mother and is a source of embarrassment for his politician father (Robert Patrick). It takes quite a few emotional stand-offs and scrapes before father-son bonding can ensue.

The film has seen its writer-director Gren Wells named as one of Variety's 10 directors to watch: previous honorees include Ben Affleck and Denis Villeneuve.

“It was very nicely written,” says Robert. “That was all there in the script when we first all read it. It treaded that line very skilfully between being respectful about mental illness and very funny and tragic at the same time.”

Still, mastering Tourette’s must have required a lot of research, right?

“Oh yeah. There was a lot of homework to do – largely motivated by terror, the fear of getting it completely wrong. I had five or six months before we started shooting, so I had a long period where I could do research.”

His performance looks emotionally exhausting.

“Yeah. You’re in constant suppression mode. That was the challenge of it. Any external force, anything that causes anxiety and fear, will cause spasms to ripple up to the surface. So you’re constantly sitting on those spasms.”

It might have required greater acting chops but The Road Within, one senses, was an easier gig than The Mortal Instruments: City of Bones. The 2013 fantasy film, adapted from first book of The Mortal Instruments sequence by Cassandra Clare and starring Sheehan, was supposed to be the new Hunger Games. Instead, the $60-million film limped away with $90,565,421.

“With those kind of movies, only 50 per cent is making and the other 50 per cent is selling,” recalls Sheehan, “and I wasn’t comfortable with that.

“ Of course you have to promote the work you’re in. Of course that’s part of the job, but this was an avalanche of press. And as we were nearing the release of the film in North America, we were made aware of numbers and quotas. You have to make this amount of money in the first weekend. It just felt weird.”

No matter – for now the world is Sheehan's oyster. He has just lately stopped off in France to shoot Moonwalkers with his Season of the Witch co-star Ron Perlman and his old Cherrybomb mucker Rupert Grint. And he has recently wrapped on the Italian holocaust drama, Anita B.

“I am very much the European jetsetter,” says Robert. “I went to Italy with this romantic idea that I would soak up Italian. The crew all spoke Italian even though the film is in English, but in the end I only managed to learn ‘I need to go to the toilet’. Ah well.”

The Road Within is at JDIFF on Sunday, March 22nd, at 8.45pm in Cineworld. Sheehan takes part in an industry event "Expressing Emotion: Actors In Conversation" on Tuesday March 24th at the Teachers Club at 3pm.