“I can’t say that I totally understood it,” admits Colin Farrell, scratching his head. The Irish actor is talking about the first time he read the script for his new film, The Lobster, a brilliantly surreal comic parable that took the Jury Prize when it premiered in Cannes earlier this year. It’s not hard to see why he struggled for even the concept is mind-bending: set in a near-future, singletons have forty-five days to find a mate or be turned into an animal and set adrift in the woods.

Directed by Yorgos Lanthimos, whose 2009 film Dogtooth was greeted with similar critical acclaim, Farrell has just seen it for the first time when we meet – and he’s still trying to get his brain round it. “It’s singularly the most bizarre thing I’ve ever read,” he says, “and it’s one of the most bizarre films I’ve ever seen.” According to him, it’s a movie that defies categorisation. “I mean more than anything that I’ve done I feel like its wide open to interpretation.”

Indeed, The Lobster is the sort of piece that’s liable to see film theory students pore over every frame. But if that sounds rather too dry, nothing could be further from the truth. Lanthimos and his co-writer Efthymis Filippou have seasoned this story with a wry and warped sense of humour. Even if he didn’t get it straight away, Farrell was laughing as he read it “and, of course, I didn’t know if I was supposed to be”. The sort of nervous laughter, he says, that often comes with confusion.

Think Bridget Jones’ worst nightmare, all set in a hotel that resembles Fawlty Towers – run by Olivia Colman’s officious manager – and you’re beginning to picture The Lobster. Farrell plays divorcee David, who arrives at a bleak guest-house on the outskirts of an unnamed city to participate in this seemingly mandatory ritual. If he doesn’t find a mate, he’ll be transformed into a creature of his choosing – in his case the titular crustacean, reasoning it has a long life-expectancy.

It’s the sort of absurdist nightmare that Franz Kafka or Luis Buñuel would’ve once dreamt up – not least as David flees the hotel in the film’s second half and joins with a band of outsiders (including Rachel Weisz) living on the fringes of society. If the film satirises our rather callous modes of courtship in the Internet age, David comes to represent mankind’s inherent isolation and loneliness, what Farrell calls “the aching humanity”, as his character goes looking for real emotional connections.

Certainly his best since 2009’s equally acerbic In Bruges, The Lobster has arrived at a fascinating juncture in Farrell’s career – in a year that’s already seen him in Liv Ullmann’s Strindberg adaptation Miss Julie and at the centre of the second season of HBO’s True Detective. His attitude to work has changed, he says. “There are things that I have read lately that in times gone by I would have certainly contemplated more than I have done in the last year. Couple of things that I may have gone: ‘It’s not brilliant but it’s good and we can elevate it.’”

This marks a significant gear-shift for the Dublin-born Farrell, who spent most of his early career rocket-propelled towards Hollywood. After a spell at the Gaiety Theatre in his teens, a breakout role in soap Ballykissangel led to a film career that exploded after he played a soldier in Joel Schumacher’s Vietnam drama Tigerland in 2000. In five years, Farrell made films for Steven Spielberg (Minority Report), Oliver Stone (Alexander), Michael Mann (Miami Vice), Terence Malick (The New World) and Woody Allen (Cassandra’s Dream).

“My head was spinning,” he admits. “All I could do was hold on and pretend that I didn’t care about any of it.” Who could blame him? The closet he’d got to fame in his youth was the fact his father and uncle both played football for Shamrock Rovers and he once unsuccessfully auditioned for Boyzone. Working with Hollywood’s crème-de-la-crème was “insane” he reflects, as he became a tabloid bad-boy for a time – a party animal dogged by sex tapes, affairs with Playboy models and rehab recoveries.

Gradually, Farrell calmed down. He became a father to two boys, 12 year-old James (the product of his relationship with American model Kim Bordenave) and 6 year-old Henry (whose mother is Farrell’s Ondine co-star Alicja Bachleda-Curus). Never married, unlike his character in The Lobster he’s stayed single of late. “I haven’t had a relationship five or six years, and I’m fine with that,” he says. “But I believe in relationships, I believe in marriage, I believe in people sharing their lives.”

Now 39, Farrell lives in Los Angeles, near Griffith Park, and evidently relishes the sun-dappled West Coast lifestyle. His hair shaved at the sides and slicked back, he looks trim today in jeans, tan boots and a light blue sweatshirt. “I certainly live a lot healthier than I ever thought I would. I wouldn’t say vanity isn’t in the building at all, but it’s not really an exercise in vanity.” He hikes and he does yoga, which he loves. “Every time I put the mat down or I even stand on it, I get excited by it. Truly.”

The thought of Farrell getting pumped by a yoga mat is quite amusing, given his wild-man reputation from the past. Heaven knows what they’d say back on the streets of Dublin. At least The Lobster, which was shot in the south west of Ireland, afforded him the chance to make a pilgrimage back there – something he’s managed to do every so often in his career for films like John Crowley’s Intermission and Neil Jordan’s Onedine. “It was paradise,” he smiles.

Does he miss Ireland? “I do, and I don’t. I don’t miss it every day,” he says. “Home, or your place of birth, has a very strong pull on your heart. But, really, children, more than anything create a home.” You can certainly detect this paternal streak in Farrell’s recent work – notably playing father to Mary Poppins author P.L. Travers in Saving Mr Banks. He’s now shooting J.K. Rowling’s Harry Potter spin-off Fantastic Beasts and Where To Find Them – arguably his first real film for younger viewers.

No longer is he so interested in investigating “the very nature and fabric of testosterone and what it does”, as he calls it, as he did in films like The Recruit and Pride and Glory back is his more alpha-male days. “I suppose that kind of stuff interests me less and less. I don’t define manhood in the ways that I used to. Maybe my definition of manhood has shifted, and therefore that’s freed me up. Maybe.” If it brings us more films like The Lobster, it can only be a good thing.

The Lobster opens on October 16.