George MacKay is having a good month. His new film, True History Of The Kelly Gang, is hitting cinemas and already receiving great reviews for its kinetic retelling of the infamous criminal gang’s saga. But he’s also just returned from the Oscars, where 1917, Sam Mendes’ epic war film in which MacKay stars, won three Oscars.

“It was grand!” says MacKay, a beloved Irish expression he possibly picked up from acting opposite Saoirse Ronan in How I Live Now. “It was mad. Amazing, overwhelming, seeing this thing you’d been a part of being recognised and celebrated. It ticked all the boxes of the experience.”

1917 is a deeply immersive film, shot in eight long takes that required months of intense rehearsal and co-ordination. It imbued MacKay with an awareness of how every aspect of filmmaking worked, from the camera men running alongside him every day, to the production designers who built miles of labyrinthine trenches. Then there were the stunt and effects teams who had to make explosions happen as he ran by.

“It was the most inclusive, collaborative experience I’ve ever had for a film job,” he enthuses. “It gave me a proper understanding of everyone’s roles. And you need that. Sometimes there’s that fabled thing of, ‘Oh to be a serious actor, you must be completely in your own head and create your own world.’ But actually, you’re all working together on the same thing, towards the same goal. So an atmosphere where there’s an awareness of what everyone’s doing makes it much more rewarding.”

But now, the 27-year-old is focused on True History Of The Kelly Gang, directed by Justin Kurzel, who MacKay has loved since Kurzel’s evocative biographical crime drama Snowtown. He had also auditioned for Kurzel’s 2015 Macbeth, starring Michael Fassbender.

“I loved meeting Justin,” the actor enthuses. “He really put me through my paces in the audition, challenging me. You can’t fake it with Justin; he wants authenticity, he wants the real thing. So I really wanted to work with him.”

But for MacKay, there was also a historical, familial attraction to the role that emerged while speaking to his Dad, who grew up in Adelaide.

“I’d never asked him about it – sometimes your parents are just your parents, and you don’t ask!” says Mackay. “But we had this long, impromptu conversation about his growing up, and also about how his grandfather had come from Ireland. He went to Australia on his own, fought in the war, came back, and lost his leg working the railways. Then he bought a pub – there were all these things I never knew, especially the Irish connection. So when a script came through that was Justin Kurzel doing a film about an Irish-Australian, it was just…” MacKay mimes a moment of divine intervention, complete with heavenly chorus.

Even though the project allowed MacKay to explore his family history, he was relatively unaware of the historical optics of Ned Kelly. This gave him space to try and understand the icon.

“Ned Kelly has become something to a culture,” he notes. “He has a meaning and an identity that is tied up in the folklore surrounding him. There are a few hard, fast facts as to what happened, when it happened, but the why is all up to the person who’s documented this.”

It’s a Ned Kelly you will not have seen before. Kurzel’s vision for the character and his gang is interpretative rather than historical, drawing from contemporary influences such as glam-rock, punk bands, and even Conor McGregor, to create an atmosphere of rebellion and swagger. It’s also intriguingly queer. Ned Kelly and his gang famously wore dresses to unnerve their rivals, but Kelly Gang leans into other queer elements, including androgynous glam costuming and a homoerotic energy between male characters. MacKay appreciated the ambiguity and complexity of these elements.

“Ned or any of the characters aren’t portrayed as being gay, necessarily. For me, it’s more about the complexity of all of their love, and that’s what I love about the film – the beautiful murkiness of all that emotion. Ned’s greatest love is his mother [played by the remarkable Essie Davis], and within that there’s a kind of sexual element. But he’s in love with his mother because he’s been made to be his Dad too soon. And his best friend Joe, I don’t feel that they’ve slept together, but they touch each other in a loving way. And in our understanding, we say ‘They must be gay’ or ‘He must be incestuous with his Mum’, but I love the undefinable nature of it.

“We didn’t commit to any labels or orientations. Justin said once ‘A fuck and a fight aren’t that different.’ The feelings that both sex and a fight evoke physically and emotionally are similar; the heart-pounding, sensual overload. But the words that define them are polar opposites, and that tension is what Ned is: he’s a fuck and a fight. He was taught love through brutality.”

MacKay pauses thoughtfully. “It’s tricky and undefinable, and I don’t have a clear answer. But for me, that’s quite true of life. We’re in a time where people are looking for definition, either in themselves or socially or nationally, and of course we need some clarity and recognition. But sometimes that clarity can be confusing, because it pigeonholes a feeling or an action.”

With such complex dynamics and interactions, Kurzel wanted MacKay and the actors playing Ned Kelly’s gang (Sean Keenan, Earl Cave, Louis Hewson) to bond and create an authentic relationship before filming. So Kurzel demanded they form a band – and signed them up to play some gigs, to make sure they took it seriously.
Well, almost seriously. I ask sweet, polite, endearingly humble George MacKay what the young men decided to call their band.

“Fleshlight” he giggles. “I don’t know where it came from! It wasn’t me!” he laughs, protesting. “Justin said if I wanted to go in on this part, we could go in. So he sent me a massive to-do list, lots of films to watch, music to listen to – a lot of Aussie punk – a reading list about the history of Ned. I went to where Ned’s Dad was from in Ireland – he was from Cashel – and I rode horses. I chopped wood for a week in Tasmania, I had some amazing life experiences while exploring the character of Ned.

“But Justin also said ‘I see these guys as a punk band, and I want you guys to learn to listen to each other. I’ve booked you a gig in a bar in Melbourne in three weeks, so you’re going to write and perform a set.’ And we did that! We went in, put on dresses everyday and jammed these songs. It was great!”

• True History Of The Kelly Gang is in cinemas from March 6.