The fact that Josh O’Connor hasn’t done a play in “11 or 12 years” is, in his opinion, “horrific”. “[Theatre] is how I started my career,” he says, smiling from his living room, where he’s sheltering from one of England’s many summer heatwaves in a green Loewe t-shirt. “That was all I ever wanted to do; be on stage.” Still, there has been good reason for his prolonged absence. During the course of the hiatus, the 36-year-old has earned himself BIFAs, Emmys and Golden Globes, a Dior ambassadorship, and a reputation as one of the best in the biz – for his work on screen but also for being a genuinely sound guy. He’s played a young Prince Charles in , a former boxer-turned-priest in Wake Up Dead Man: A Knives Out Mystery, a washed up tennis player in , and an alien whistleblower in – to name just a few particularly sparkly entries on his glittering CV.

So, , directed by Sam Yates at the Almeida Theatre this month, feels like a rather fitting way for O’Connor to return to his old love. Clifford Odets’s 1937 drama – “an incredible play” but by no means “easy or perfect”, Josh says – follows Joe Bonaparte, a gifted violinist who is seduced by the prospective fame and fortune of professional boxing, leaving him torn between the life he could have and the life he is being encouraged to build.

“It’s not a gentle reintroduction to theatre,” jokes the actor, who has been juggling boxing classes and violin lessons in order to play Bonaparte since he wrapped on his last film project, Alice Rohrwacher’s with Saoirse Ronan, Dakota Johnson and Jessie Buckley. “I’m excited. But I’m terrified.” O’Connor first met Yates after seeing his production of , starring his friend Andrew Scott, and the pair read through half a dozen plays together before landing on , though they initially wanted to rule it out. But in the end, its imperfection was part of what drew O’Connor in. “For one thing, I like a problem. I like finding a solution to something and finding a way to tackle a piece of text.”

O’Connor’s character is brilliant at two things – violin and boxing – but where the latter offers him the money, fame and status of the “capitalist dream”, the former represents creativity, and a chance to pursue his true passion. “What makes a good life?” O’Connor asks of this conundrum. “What makes a life worthwhile? Is it money and power or is it discovery and community and art?” Questions that are as pertinent today as they were 90 years ago when the play was written, and perhaps especially so for a man who has gone from theatre actor to fully-fledged movie star. “I don’t think it’s quite so linear as films and television are bad and theatre is good,” he continues. “I’m very fortunate. I love making movies.” But, he concedes, what interesting, is the constant pressure towards “more and more and more” – more money, growth, possessions – and how chasing those things leave less room for pursuits that are purely about enjoyment.

was an ambitious choice. O’Connor will box and play violin on stage. The music, he admits, is the bigger challenge. He played from aged eight to 11 but remembers being “terrible at it”, and his parents recently confirmed his suspicions when he asked them why he stopped. “They said, ‘We asked you to.’” His neighbours are now getting used to the sounds of his retraining. “Violin sounds horrible unless you are really good,” he says, laughing. “And so my poor neighbours here are furious.”

He is also working on an Italian-American accent – he is used to them – and the period setting is providing some additional comfort. “If it’s a bad accent, I can just be like, ‘Well, you weren’t there in the 1940s, guys. That is how they sounded.’”

Away from rehearsals, O’Connor is spending what spare time he has doing the thing he is perhaps most excited about: gardening at his home in Gloucester. “My dream right now is to have one calendar year where I do everything that you’re supposed to do in a garden and experience it for a whole year,” says the star, whose usual schedule means long periods away from home on set. So far, he has managed to eat one cabbage (though he grows all manner of things). He is currently reading by Monty Don (“the David Attenborough of gardening”), and learning how he and his wife Sarah left a successful jewellery business for gardening has struck a particular chord. There’s a faint parallel with Joe Bonaparte: a man who eventually chooses the thing that gives him a sense of purpose over the thing that makes him successful.

For all of the big questions tackled in , it is the routine of a theatre gig that O’Connor is particularly excited to rediscover. “I’m really excited to be in the UK and doing a play and maybe having the odd day to go to a gallery or read my book,” he says. The last time he performed regularly, at the RSC in Stratford-upon-Avon, his life revolved around what he (and possibly many other actors), call the “Triangle of Death”: his house, the theatre and the pub. This time around, he suspects he will be going home after performances to sleep and read, rather than trying to catch last orders, but O’Connor is looking forward to being rooted in place, and hopes to one day do it again at the RSC – still among his favourite places to perform.

While explores the pressure to capitalise on talent, the work itself offers something more: the opportunity to pick back up an instrument abandoned in childhood, get punched on stage, read books, and eat more than one cabbage from his bountiful garden.

Golden Boy is at Almeida Theatre until 31 October and will be released in cinemas via National Theatre Live from 5 November