Eoin O'Brien never thought that moving to Bangkok would lead to a career in action movies. He had originally been drawn to Thailand by the offer of a job as a fitness instructor and sports coach. But now the Dubliner squares off against martial-arts stars, choreographs stunt moves and plays an assortment of bruising characters. That might sound like an unconventional transition, but the 38-year-old says his life has been filled with stepping stones that make sense to him only now.

"If we go back to the beginning," O'Brien says, "it started when my dad brought home a copy of The Karate Kid. I was about seven or eight, and I just became enamoured with this skill that could elevate you above the norm and empower you to fight off bullies."

He began to idolise Bruce Lee, the Hong Kong-born martial artist and actor, wanting to study kung fu just as his hero had done. But the only option was karate, at the local leisure centre in Portmarnock. After a couple of years he had to face a local bully in a tournament. "Even though I was still a kid I nearly knocked him out with a kick. I didn't have any problems with bullies after that."

O’Brien studied every martial-arts film he could find until, eventually, another passion took over: basketball. He played for Ireland at underage level, which led to a scholarship to the US and a series of stints playing professionally in Europe.

By the time he was 31 O’Brien was playing for Killarney’s national-league team and wondering whether it was time to do something else. That’s when he took a holiday to Thailand, visiting a friend who was a school principal there. At the end of the trip, his friend had a proposal: “Move here, coach at my school and crash at my place until you have somewhere of your own.”

It wasn’t a hard sell. O’Brien felt an attraction to the weather, the food, the people and, perhaps most of all, muay Thai, a form of Thai kick-boxing also known as “the art of eight limbs”. “I’d picked up martial arts again during my time in Kerry, taking a weekly class in MMA [mixed martial arts], wrestling and jujitsu,” he says. “So I was determined to train in muay Thai as soon as I got to Bangkok [in 2008]. But I knew you couldn’t just walk into a gym thinking, I’m in Thailand, so I may as well fight. You have to respect the sport and train hard. Otherwise you’ll just get your ass handed to you.”

O’Brien trained for two years before his first professional fight, going on to win four out of four encounters. “It can be quite nerve-racking,” he says. “But you see these Thai kids there, and it’s nothing to them. It’s like playing a game of football. So that gives you confidence – ‘This guy’s not scared, so why should I be?’ It’s such a tough sport, but the sense of accomplishment from conquering your fear and overcoming that situation is immense.”

Lead villain

During his second year a production crew visited his gym, looking to cast the villain for a film called

Fireball Begins

. They chose O’Brien. “It was basically about people playing basketball and kicking the crap out of each other at the same time,” he says with a laugh. “So it seemed like the perfect role.”

O’Brien had little experience as an actor, let alone as a stuntman. His time in front of a camera amounted to an Irish Water Safety ad and a role as a street urchin alongside Twink for an RTÉ Christmas special. But rehearsing with professionals made him realise that he had picked up some relevant skills along the way. Rehearsing fight scenes wasn’t all that different from relying on the mechanics of a practised move in basketball, for example, or learning to control the pain factor in muay Thai.

The Fireball Begins project collapsed – "It turned out they didn't have funding for the whole movie" – but the experience got O'Brien hooked on acting. He realised that Bangkok has a burgeoning action-cinema scene comprised of a relatively small community, so he began to attend castings for commercials, films and stunt work, to build up a portfolio. "You have to prove yourself job by job," he says. "Even if it's just an ad it's all experience on set. It's all performing under pressure and building confidence. You give 100 per cent not just for that moment but for the chance to be in future projects with the same people."

The more that momentum grew the more O'Brien had opportunities to hone his skills and build a showreel. Eventually he was cast in the 2012 film Kill 'Em All, alongside Gordon Liu, the Hong Kong action icon behind the Shaolin and Wu-Tang kung-fu movies O'Brien had loved as a child.

“I had idolised Gordon Liu,” he says. “So when they told me I was going to be his right-hand man I was just like . . . I couldn’t believe it. I always dreamed of doing this, but I didn’t see how it was possible. Growing up in Ireland, how do you start working in martial-arts cinema? If you go to Hollywood you could be one in a million going to auditions while working as a waiter. I never thought this was a realistic career option until it landed in my lap.”

Plenty of highlights have materialised since. Some have taken O'Brien in unexpected directions, like flying to Los Angeles for a small part in Guillermo del Toro's Pacific Rim or playing an Irish drug dealer in the Danish series The Legacy. Among forthcoming projects, Jason Statham throws a fire extinguisher at O'Brien's head in Mechanic: Resurrection, Michael Jai White gives his ribs a good kicking in Never Back Down 3, and O'Brien goes head to head with Steven Seagal in Asian Connection.

It feels funny, he says, reflecting on the serendipity of it all. Without a basketball scholarship he wouldn’t have earned a degree in sport sciences. Without that degree he wouldn’t have landed the job in Thailand. Without Thailand he wouldn’t have become a muay Thai fighter. Without muay Thai he wouldn’t have been cast in a film.

For job security between roles O’Brien teaches English to university students in Bangkok, where he is based, which affords him the flexibility to train and take on filming projects. He has also stopped fighting professionally, to avoid injuries that could put him out of commission, instead focusing his efforts on writing scripts of his own.

“My aim is to keep progressing, keep developing my skills,” he says. “Ever since these opportunities arose I’ve thought, Well, maybe I am on the right path here; maybe this is what I was supposed to do all along. I’d love to be producing, writing, even directing full time. That’s the dream. It’s right there in front of me. I just need to make it happen.”