I can think of no more perfect visual metaphor for Chris O'Dowd's booming career these days than his own appearance at last year's Cannes Film Festival: walking the red carpet for the midnight premiere of Australian musical comedy “The Sapphires,” the 6'3'' Irish comedian looked every inch the Hollywood star in a sleekly tailored tux, his unruly mop even combed tidily into place, conforming to the code of an A-list world in which, only a few years ago, he would have been a distinct outsider. Well, almost conforming. Keen-eyed sartorialists would have spotted a flash of yellow just above his polished dress shoes: a dashing pair of bumblebee-striped socks.

O'Dowd's funky choice of hosiery seems indicative of a career in which his unlikely ascent to the top has come very much on his own terms. From modest beginnings in Irish television to his breakout role in popular UK sitcom “The I.T. Crowd” to his star-making big-screen turn as Kristen Wiig's love interest in “Bridesmaids” and beyond, the personable, handsome-but-not-Hollywood-handsome actor has attained crossover success with compromising his image, his persona or even his endearing Irish brogue.

Since “Bridesmaids,” his US profile has steadily risen, with supporting roles last year in “This is 40” and “Friends With Kids,” as well as a multi-episode run in red-hot HBO comedy “Girls.” This year, meanwhile, is building on that still further: in May, we'll see him as the lead in another buzzy HBO show, Christopher Guest's mock-doc “Family Tree,” while his appearance in superhero sequel “Thor: The Dark World” has only just been announced.

Tomorrow, meanwhile, US viewers will get to see his first big-screen lead role in the aforementioned “The Sapphires,” the loosely fact-based story of a female Aboriginal soul quartet who found fleeting stardom entertaining Vietnam troops in the 1960s. Despite the title, it's O'Dowd, playing their passionate but alcoholic manager Dave, who's the star of the show: it's a forceful comic turn that gives this sweet, sometimes over-sweet, crowdpleaser its true, well, soul. An awards campaign – remember this is a Weinstein Company property – would not be out of order for a performance that reveals his gifts in a project we wouldn't necessarily expect him to headline.

“It was a bit of a surprise to me too!” he exclaims over the phone from New York – “The city of apples,” he quips dryly – where he's publicizing the film. “It was just one of those things: the week after 'Bridesmaids' came out, I was sent a few scripts and, to be honest, a lot of them were just typical rom-com fare, without the style or quality of a 'Bridesmaids.' So I made the decision to go off and do something quite different, maybe get out the country for a bit. And just then I read 'The Sapphires' and it jumped out at me – I felt I hadn't seen that world before, and I love that era of music. And the script was funny, which is rarer than you might imagine.”

Funny as the script was, it still required some tailoring for its quirky leading man: the character as written was Australian, for starters. Luckily, director Wayne Blair and writer Tony Briggs – who penned the stage production on which the film is based – were flexible. “We did make a few changes, to make Dave a bit rougher around the edges: we made him Irish, we gave him a bit of a drinking problem” – he offers an apologetic pause at the cultural stereotyping – “so we gave him something to fight against. I like the ambition of Dave, the way he believes that he can change the world even when he's staring defeat in the face and living in his car. I relate to that.”

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.