The sun was setting on an early spring day at last year’s Sundance Film Festival. But there was a long night ahead for several of the film industry’s most high-profile rights negotiators. The rapturous applause following the screening of Manchester by the Sea was enough to set the wheels in motion: this film had Academy Award written all over it.

Next followed an all-night bidding war where eventually the new kids on the block from Amazon Studios won out – beating the likes of Sony, Universal Pictures, Fox Searchlight and Lionsgate – to win the US distribution rights to the film. It was the second largest purchase of the whole festival.

The film’s leading man, Casey Affleck, might not have graced as many glossy magazine covers as you’d expect for someone who has been working in the industry for more than 20 years – but that’s the very reason we wanted him to be on ours.

Up until now, you would never have said Casey Affleck was the ‘obvious choice’. Growing up with Ben as his older brother ensured that. But if Ben is the headline-grabbing, finely-buffed Ferrari 250 GTO, Casey is the more understated 275 GTS: arguably more elegant, certainly more of a cult hit, but not a thoroughbred trophy snatcher.

Indeed, so far an Academy Award has alluded the younger sibling. Even upstaging Hollywood titan Brad Pitt didn’t prove enough to manage it. He was within a hair’s breadth of an Oscar for Best Supporting Actor for his flawless portrayal of Robert Ford in The Assassination of Jesse James by the Coward Robert Ford back in 2007.

“I did an enormous amount of research for that role,” he explains to me as we chat in the run up to Thanksgiving last year. “I started by reading old nickel and dime books about Jesse James, the James gang, and the Wild West in general. They were the kind of books that someone on the East Coast would have gotten their hands on – and those stories would have contributed to a distorted ethological vision of what the James gang was. It’s what Robert Ford would have read. I read newspaper articles from the period every single day – in the morning, in the trailer. Some of that stuff I used in the movie,” says Affleck.

Although Affleck admits he doesn’t go full Daniel Day Lewis with his method acting, he does embody the roles he plays with an undiluted intensity. Despite this, his gripping portrayal of Ford wasn’t enough to secure him the Oscar back in 2007. He lost out to Javier Bardem for his terrifying performance as Anton Chigurh in No Country for Old Men. Frankly, no one had a chance against him.

But this time around, his chances might be better. Affleck has been hotly tipped for the big one – Best Actor – for his portrayal of Lee Chandler in Manchester by the Sea. It looks like only Denzel Washington could get in his way. The film is a touching and tragic story, which sees Affleck’s character lose his brother, and receive legal guardianship of his nephew.

“He’s experienced a lot of tragedy in his life, that’s already left him pretty scared,” explains Affleck. “And being back in his hometown is difficult for him. However, after the death of his brother, there’s no one left to take care of his nephew, and so there’s a collision of his sense of responsibility and his very strong desire not to confront his past. That’s the conflict, really – that’s the centre of the movie.”

Originally, the film was due to be directed and starred in by Matt Damon – a long-time family friend of the Afflecks. In one of Casey’s first films he played a buddy of Damon’s in Good Will Hunting alongside brother Ben. But because of scheduling clashes, Damon made way for Casey: “Matt was already shooting another movie” Affleck explains. “In the end he really wasn’t that involved. But he was key to the initial development of the script – and asked Kenny to write it,” says Affleck.

There isn’t any sibling rivalry with Ben; I think we have very different, very individual career paths

Despite some controversy surrounding his previous film, Margaret, screenwriter and director Kenneth Lonergan was top of Damon’s list to take the reins for this project. Lonergan worked on the screenplay for You Can Count On Me (two Oscar nominations); Gangs of New York (ten Oscar nominations) and Analyze This (er, zero Oscar nominations, but $176.9m in global box office takings.)

Affleck was more than convinced: “Kenny is my favourite kind of person to work for and with, because he really likes to talk about stuff the way that usually only other actors like to talk about it. You know, why people say the things they say? Why are they behaving this way? What does it mean if your character sits down in a scene, versus standing up in a scene? These teeny, tiny, little details that just make other people sort of shrug and squint at you, he enjoys talking about, almost as much as I do,” explains Affleck.

The script really resonated, too: “What I thought, was, this was really beautifully written, it’s very moving, it’s really funny. It’s seemed very personable and believable, intimate and universal at once,” he says.

“This is what you dream of working on when you first become an actor. And to be working with a team this dedicated and talented, you feel secure and safe to explore heavy material like this, you feel safe driving down that road where you can lose yourself. I knew Kenny was looking after me the whole time and that felt very comforting.”

This is the second time that he’s worked with Lonergan – the first time was here in London: “He’s an old friend. We started working together in a play in the West End, at the Garrick Theatre, called This is Our Youth. It was one of his first great pieces of writing. We became good friends, and stayed good friends since,” he adds. Affleck starred alongside Matt Damon and Summer Phoenix in the show, which proved West-End gold dust: a play that actually managed to attract young audiences.

Not one to be pigeonholed as an actor, Affleck has branched out into writing and directing, too – most famously in his 2010 mockumentary I’m Still Here. Starring his former brother-in-law Joaquin Phoenix, the film purported to follow the life of Phoenix, starting with the announcement of his retirement from acting, through his transition into a hip-hop artist. That is except the whole thing was a giant hoax. It was post-modernism on another level. But the film’s art was lost on the majority of critics and audiences alike.

However, Affleck has learnt to take the rough with the smooth in his career. The I’m Still Here backlash hasn’t deterred his aspirations. When it comes to his next project – Light of My Life – Affleck is writing, directing and acting in it. Although, when pushed on his favourite of the three disciplines, he pauses and admits “it has to be acting”.

Affleck often plays edgy, raw characters – rarely opting for the epic pin-up roles. Take Out of the Furnace, where Casey’s character, Rodney Baze Jr fights in illegal bare-knuckle brawls just to pay the bills. Baze is a former US Marine, who returns from the war a victim of post-traumatic stress disorder. It’s a commanding performance, but like much of his work, it’s not necessarily comfortable to watch.

And the same can be said about his performance in Manchester by the Sea. He delivers as much in the big moments as he does in the small ones. It’s refined, sophisticated acting which sucks you in. It’s not obvious – and it’s not easy – but then, the road to a Best Actor Academy Award never is. Could this finally be Affleck’s big moment?

Affleck on Affleck

“It’s been great having Ben in the industry. It can be difficult to navigate this business; there’s highs and lows and I’m lucky enough that I have my brother and Matt [Damon] who know what it’s like and have been through it, too. There’s an understanding, which is comforting because it’s hard to describe to someone who doesn’t exist in that world. There isn’t any sibling rivalry; I think we have very different, very individual career paths and have never really thought that way. He’s my brother, I only have one, and we’re very close. We wouldn’t ever allow that stuff affect our relationship.”

Manchester by the Sea is in cinemas from 13 January