The role marks another significant notch in Courtney's blockbuster belt, which includes Divergent, The Water Diviner, A Good Day to Die Hard opposite Bruce Willis, Angelina Jolie's recent pet project Unbroken and Marvel's upcoming Suicide Squad.
But although at 29 he may be busy working with Hollywood heavyweights and walking red carpets with Brad Pitt, the Sydney native credits his humble beginnings in New Zealand for his success.
Courtney played Varro in Spartacus, during which time he moved to Auckland and formed a pivotal bond with the series' star, Andy Whitfield.
"Spartacus gave birth to my aspiration and ambitions to do this properly.
"Back in drama school I wasn't afraid to say that I wanted to have a crack at LA, but working on that show really offered me the experience and relationships to see how it was possible.
"Andy Whitfield was instrumental in developing a sense of ambition in me. He
had come to the States several times and, as a mate, I just wanted to know what it was all about.
"I knew nothing about the road to success.
I thought when the phone rings, you go along to the audition and just see what happens.
"Without his guidance I wouldn't have been able to see how this is possible. And the training on that job was incredible.
"You can study all you want but without feedback and getting it wrong a bunch of times, you don't learn. Spartacus had incredible reach and a really loyal fan base and I'm grateful for that."
With only bit parts on Aussie series like All Saints and Packed to the Rafters before Spartacus, Courtney cashed in on the New Zealand project's global success with a move to Los Angeles, where a role opposite Tom Cruise in Jack Reacher set his US career in motion.
He has since starred in a steady string of films, but admits his rapid success comes with challenges - the biggest of which is working out how to maintain that momentum.
"It's interesting because I was relatively inexperienced in Australia, so I didn't feel like I had honed my craft before coming to the States. Most of my growth as an actor has happened overseas and it sounds cliched, but just working in this industry is the biggest challenge.
"You deal with expectation - your own and that of those around you. And when you start to get opportunities and chalk some films up, it doesn't actually get any easier.
"I remember when I was working on Die Hard, a mate asked, 'Are you just chilled now? Are you relaxed?' implying I didn't have to fight for things any more and that the struggle of being an actor was over.
"If anything, I'm even more tense and nervous about the next move and that's what happens when you start to gain exposure.
"You're worrying about things that never occurred to you when you were unemployed because you were just trying to get a job. All of a sudden, you're dealing with, 'What's the right move to make next? What is it saying if I go and do this film? Is it going to hurt my career if I take that job on?'
"This is a very fickle business. If you make the wrong move several times, you run out of chances. So that's the hardest part about starting a career - trying to keep one afloat."
Carefully contemplating the projects he takes on, Courtney will next star in Suicide Squad, but plans to steer away from doing more action roles.
"I made a decision a year ago that I wanted to start focusing on material more. I've had the fortune of doing a bunch of action and don't necessarily want to leave that behind, but break things up and get less focused on the size of the role or scale of the project, and more on the character and working with great filmmakers."
Cue Angelina Jolie, who came through with such a role for Courtney while making her Oscar-nominated film Unbroken.
He auditioned for five characters in the film, based on the story of Olympian-turned-war-hero Louis Zamperini, before being cast as World War II pilot Hugh "Cup" Cuppernell.
He admits to nerves before meeting the actress for the first time, but word on the movie's Australian set was that Jolie was nothing short of "wonderful".
"Of course, with someone like that, who has such notoriety, you have a sense of expectation or apprehension.
"You don't know what they're going to be like, but I had been out for beers with a few of the boys before and there was this unanimous opinion that she was wonderful and chilled - and that was the case.
"She's a warmhearted, open-minded, generous, genuine individual, who really is intelligent and caring.
"I would love to work with her again - on one or both sides of the camera."
