EDINBURGH - As we sit down in the appealingly tatty coffee shop of Edinburgh's Filmhouse – the stone-built base camp of the city's venerable film festival – Chad Hartigan admits feeling pleasantly bemused at being interviewed for In Contention. As well he might do. It's not that long ago that Hartigan's name appeared in bylines rather than headlines on this site – one of several where he plied his trade as a box office analyst for five years, while laying the foundations of an independent filmmaking career. 

I'm half-tempted to ask Hartigan for a projected gross for his own film; after all, it's not every scrappy indie writer-director who can boast such cool-headed commercial instincts, even (or perhaps especially) with regard to blockbusters fare a million miles from their own. “A lot of people wonder if all that work has given me some kind of like secret code,” he says, with a dry laugh. “Like I could make the failsafe blockbuster. After five years, I still don't know what exact science makes a hit. But I do know that 'This is Martin Bonner' is not it.”

He's being both modest and entirely honest: “This is Martin Bonner” is Hartigan's second feature film, and you'd struggle to make a more thorough counterpoint to everything that contemporary studio cinema seems to stand for. A gentle but clear-eyed character drama predicated on unfashionable notions of faith, charity and humble human goodness, its title character is a lonely, middle-aged Australian expat, recently relocated to Reno, who finds purpose and companionship as a volunteer for a prison rehabilitation program.

Its narrative is one of small, significant gestures rather than dramatic incidents; the friendship that develops between Martin (Paul Eenhoorn) and weatherbeaten ex-con Travis (Richmond Arquette) surprises mainly through its lack of typical conflict. It's that unassuming but confident serenity, its unsentimental but unusually positive human oulook, that made “This is Martin Bonner” stand out against conceptually flashier rivals when it debuted at the Sundance Film Festival in January, winning an audience award an initiating an international festival run – Edinburgh, where we meet in June, marked the start of its European leg – that has exceeded Hartigan's wildest initial expectations for the project. Ditto a slow-burning theatrical release in the US that today reaches full fruition, with the film hitting theaters in New York and Los Angeles.

“It's just been a dream,” says Hartigan, not a man given to gushing. And even without theatrical distribution, the film's festival reception would still have floored him. “That's something I aspired to more than any theatrical success. I felt, for this movie, dreaming about theatrical success would be a fool's errand. But dreaming of festival success was attainable.”

Still, he wasn't expecting the endorsement of the flagship festival for independent film. “Sundance absolutely made this movie. I don't think it would be here if it didn't get into Sundance. I feel like it could very easily have fallen through the cracks and nobody would have played it. It really needed somebody to stand up for it and say, 'This is worth some attention.'”

Hartigan knows from experience how hard it is for films like his to get that attention. His 2008 feature debut “Luke and Brie Are on a First Date” – made while he was still on box-office patrol – was a smart, spiky romantic comedy of sorts, expressly based on one of his past relationships, that played some smaller festivals, but never found US distribution. Its greatest, and unlikeliest, success was spawning a faithful Argentinian remake after appearing in a festival there, a progression that Hartigan describes as “surreal but cool”: “It contains lines that were verbatim from that movie, which in turn were verbatim from my real-life date. They don't really belong to my personal memory anymore. It's kind of like a distant memory that has been usurped by the movie.”

Guy Lodge is a South African-born critic and sometime screenwriter. In addition to his work at In Contention, he is a freelance contributor to Variety, Time Out, Empire and The Guardian. He lives well beyond his means in London.