Addicts, immigrants, the rural poor, teenage mothers . . . Film director Lenny Abrahamson is making a name for himself with his vivid portrayal of the lives of the marginalised. He tells Michael Dwyerhow he has moved from town (Adam & Paul, Prosperity) to country for his award-winning new movie Garage), but his interest in those living on the edge remains.

Prosperity, the gritty and affecting social drama series, comes to the end of its run on RTÉ next Monday, a week before the Irish cinema release of Garage, which, like Prosperity, is written by Mark O'Halloran and directed by Lenny Abrahamson. Garage, a recent Cannes prize winner is the second feature-film collaboration between O'Halloran and Abrahamson after Adam & Paul.

Made on a low budget of €400,000 in 2004, Adam & Paul is a moving tragicomedyfeaturing O'Halloran and Tom Murphy as hapless Dublin heroin addicts. It was critically acclaimed on the international festival circuit and became a surprise commercial success in Ireland.

"I think it's the only film that took more at the Irish box office than it cost to make," Abrahamson says with a smile. "I was expecting it to do a few weeks at the IFC and some people might go out of curiosity to see this strange Kaurismakian, Beckettian, Laurel and Hardy film about junkies. It was extraordinary that it did so well."

Abrahamson, who is 41, grew up in "nice leafy suburbia" in south Co Dublin. "My parents are second-generation Jewish immigrants. My mother's father came from Poland in the 1930s and was a kosher butcher on Clanbrassil Street. My father's side were from Odessa. His father became a doctor. When my parents were born, the emphasis, particularly for my father, was to get a profession, so I don't think there was an option or a possibility of doing anything other than that, such as the arts, although my family always had a great love of music. My father's a lawyer and listens to music all the time."

While studying philosophy at Trinity College Dublin, where he graduated with first-class honours, Abrahamson met future Garage producer Ed Guiney and they founded the college video society.

"I'd always been really interested in cinema," he says. "I had all these crazy, intense adolescent ambitions, and cinema kept cropping up in them, but back then there was no obvious way of getting into film. It was like this big blank edifice with no door. Ed suggested setting up the video society, just around the time when it became possible to get the basic equipment. We managed to raise £2,000 and we made 3 Joes."

A droll black-and-white comedy, 3 Joes won the Best European Short Film Award at the 1991 Cork Film Festival, while Abrahamson was doing post-graduate studies in philosophy at Stanford University. "I was living in a trailer in California at the time and feeling down when they all called me from Cork with the news and I felt exhilarated."

Still, the gap between 3 Joes and Adam & Paul was 13 years. "By the time I came home from California, I had decided I wanted to make films. I spent about five really miserable years when I just tried to write. I think I got myself into a heap by having such high expectations of what I would do next. One script I wrote was for a feature, which was supported by the Arts Council and people were very keen on it, but I just went off it. I'm glad now because I don't think I was ready for it. After that, I started making commercials."

Returning to movies with Adam & Paul, and going on to direct Garage and Prosperity, Abrahamson has become identified with socially-concerned themes far removed from his own suburban background.

"I'm very aware of that," he says, "and of the danger of becoming typecast, although Garage is very different from Adam & Paul and Prosperity, and not just because it's in a rural setting. My interest is in exploring the possibilities of film-making. It's not campaigning political activism.

"In terms of content, those three projects have had a lot to do with the interest Mark and I have in marginal characters, whether in an urban or rural context. When I turn to films about other social strata, I will probably gravitate towards marginalised characters again. But it is very interesting how much vitriol can come from some quarters of the press about what we do. There have been a few pieces about Prosperity as middle-class self-flagellation and how it's supposed to make us all feel guilty, but that tells you more about the journalists than about us. I don't feel remotely guilty."

Was he disappointed that RTÉ scheduled the first episode of Prosperity opposite the controversial documentary on Fr Michael Cleary?

"I'm amazed by the scheduling. There are lots of really good people in RTÉ and there are plenty of them who are really annoyed about the scheduling. I think only the schedulers are not annoyed about the scheduling. I think their reasoning was to get everybody talking about RTÉ after the first night of the autumn schedule.

"The Cleary programme was going to wipe anything else out, and more than half a million people watched it. We got 187,000 viewers, which was very good against that kind of competition because 220,000 is about the average for drama on RTÉ2. The other problem, though, was that a lot of people thought that Prosperity was a serial and that they had missed the first episode, so we lost those people for the rest of the series."

Garage, which was shown in Cannes before Prosperity began shooting in May, was written with the comedian Pat Shortt specifically in mind for the central character. Josie is a lonely, good-natured, small-town misfit, and Shortt's subtly expressive performance is revelatory.

"I had worked with Pat on commercials for Eircom and People in Need, and I really liked him," Abrahamson says. "When Pat's face is at rest, there is a certain vulnerability to it, and he's also an amazing physical performer. I was worried he wouldn't do Garage. For him, it's a very big risk. But as long as his fans don't go in thinking it's Killinaskully, I think they will get a lot out of it."

The dialogue, which consistently rings true, is used sparingly in Garage, a film where silence speaks volumes. "In what I have done so far, my impulse has been towards the very minimal, pure approach. I wanted to film it in an intensely unselfconscious way, so that the audience only ever feels that they are watching the scenes unfold, as though they are a chronicle of this character's life.

"For the first two-thirds or so of the film, you are allowed to view Josie through the eyes of the town, as the harmless idiot, and not only does the cut to the events that follow signal a change, but also the style of film-making very subtly changes so that it becomes increasingly difficult to objectify him like that and you start to participate in his life with him."

Looking ahead, Abrahamson is discussing projects with Mark O'Halloran and working on screenplay ideas of his own. One draws on his experience in commercials. "It's called Adsville. It's about the shoot in Colombia for a men's facial product commercial. It deals with the midlife crisis of a guy whose relationship has just broken up and he's got to go away and shoot this ridiculous thing for people he hates."

So is Abrahamson going to bite the hand that has fed him? "I may be. It better be successful, or I'm really dead. The great thing about the advertising people is that they'll see all these hateful people and they'll say: 'Well, it's obviously not me'."

Garage opens on October 5th