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.”

A comic writer in his own right, O’Dowd was also given the freedom to create some of his own riffs for the character, both in advance and on the set: a key early speech, in which Dave explains the emotional link between soul and country music, was written by O’Dowd in the week of shooting. “I wrote a few bits and pieces that I thought would connect things up a bit in the character, and that worked well,” he explains. “And I was lucky enough to be able to improvise in other areas, which is how I like working.”

O’Dowd was pleased to find not only his director up for his irregular approach, but his leading lady too: Australian character actress Deborah Mailman, who plays the flinty mama bear of the girl group, and enjoys a tangy romantic chemistry with O’Dowd. “We just got on so well from the off,” he says fondly. “I’ve been a big fan of her work, which was one of the things that drew me to the film: she’s such a present actress. And because I do improvise a lot, it’s great to work with someone who’s capable of going with you on stuff – even in the middle of quite a dark scene, I’ll suggest that we start dancing, and she’s so responsive and quick off the mark. That was joyful.”

The musical element of “The Sapphires” was another appealing challenge to O’Dowd, who reveals a lusty, appealingly imperfect singing voice in the film. “I don’t think anybody feels as strongly about soul music as Dave does, but I do love it,” he says. “You know as you go through different stages of your life, you listen to varying kinds of music. And as it happens, when the movie came along, I was going through a big Sam Cooke phase – listening especially to his more gospel-y stuff. His album ‘My Gospel Roots’ is one of my favorite albums of all time. And anyone who was 14 or 15 in Ireland when ‘The Commitments’ came out, as I was, will forever be a soul fan.

“And the singing was fun. Soul music is great because it’s not necessarily about being the most melodic singer in the world – this isn’t Michael Bolton territory. Sing with your heart and it doesn’t really matter.” So he sold it on sheer force of personality? “Yep,” he says modestly. “That’s what I’m building a whole career on!”

He’s only half-joking. O’Dowd knows he doesn’t look or sound much like a leading man in the classical sense, but he sees that as an asset in the industry these days. He’s not wrong: just ask the many women (and men) who swooned to his klutzy, down-to-earth charms as a lovelorn police officer in “Bridesmaids.”

“I try not to think that I’m playing a romantic lead,” he says of his roles in that and “The Sapphires.” “That’s the curse. When you watch those kind of movies, you can tell when an actor is thinking, ‘Oh, here comes the close-up, I’m going to do my sexy face.’ And we’re past all that: women don’t even like that kind of glossed-over bullshit anymore. The shows and films that are popular now are much more honest stuff: look at ‘Girls.’ There’s a kind of brutality, a bit more truth, in the way we enjoy things now. You can be a chubby, dishevelled leading man these days. If you want a Ken doll, go to a fucking toy shop.”

O’Dowd claims not to have expected, or even planned for, his newfound US success: the luck of the Irish, he says, is very much on his side. He laughs: “I promise you I’m as shocked as anyone at the way things are going for me right now, and I’m enjoying every minute of it.”

Which is not to say he found himself across the pond entirely by accident: when the actor felt he’d hit something of a ceiling in the UK, and with “The I.T. Crowd” – which also launched the career of actor-filmmaker Richard Ayoade – he decided to give the land of opportunity a whirl. “There was a tipping point, sure,” he says. “The British film industry is hard, and for whatever reason, when you succeed in TV comedy in the UK, it doesn’t necessarily translate to film projects the way it does here in the US. It’s almost like they’re two completely different identities, and the TV comedy stuff isn’t appreciated by people who make arty period movies, which are abundant in Britain.

“So I felt I needed to move out to keep things moving forward. I could have done another sitcom at home, but what would be the point? I love the one that we did. So it got to a point where I thought, ‘Okay, I’ll go give it a try over there,’ but I didn’t realize it would work out so well. I was just hoping for it to get a bit better. And then it got a lot better.”

O’Dowd fully subscribes to the popular maxim that we’re in a golden age for television right now, which is why he has no intention of leaving the small screen behind, even as his film career takes flight. On top of “Girls” and “Family Tree,” he’s the creator and co-writer of oddball Irish sitcom “Moone Boy,” in which he plays the imaginary friend of its misfit pre-teen protagonist. (Imagine Hobbes in human form, and you’re halfway there.) it’s found a cult following in his homeland and in the UK, and he’s in the middle of writing the second series, which shoots in the summer. He’ll also take his first stab at directing a few episodes, and says he intends to spends more time behind the camera as his career moves forward.

“It’s true to some extent in Britain, but in America in particular, the movement between TV and film is just so much more fluid now,” he says excitedly. “I think 10 years ago or so, when more big-name Hollywood actors started making TV shows, it made a big difference. You know, when the Alec Baldwins and Martin Sheens of the world moved over, it showed audiences and the industry that you can come and go.”

Having established himself as a comic force to be reckoned with in both media, does he have much interest in pursuing more dramatic projects? It’s a route he’s taken before – among his early roles is a brief turn in Mike Leigh’s “Vera Drake” – and intends to take again, though he confesses to being “not that bothered” about it.

“I don’t know why there is this fascination with comedians ‘going serious,’” he continues. “I believe there’s drama in the comedy that we do. And a lot of range, too: there’s a world of difference between a punchline or gag-based show like ‘The I.T. Crowd’ or more honest, character-related stuff like ‘Girls.’ And then ‘Family Tree’ is a whole different thing again. So there’s already a lot of movement in the genre. You don’t have to abandon it for something where you get to cry a lot.

“I wonder whether great dramatic actors are often asked when they’re going to do a comedy – not as often, I suspect, and that’s a bit of a shame. I know from experience that comedy is a lot harder. I’ll do a drama if something good comes up, but not for the sake of doing one, you know?”

Spoken like a star with his feet on the ground. In bumblebee socks.