The golden eagle bucks the arm of its handler and looms over a frightened, fascinated crowd. No one wants to get too close, but everyone wants to get closer. The bird's been groomed and polished, paraded through the lobby of the Hotel Martinez in Cannes. The eagle is something wild in the middle of five-star sophistication. A menagerie of hustlers and hecklers crowd the entrance hall, scratching around for celebrity.

Guy Pearce is perched, high above the throng, on the roof terrace. He's being groomed and polished too, paraded in the service of The Rover, the new film from Animal Kingdom writer-director David Michôd. It's a story of savagery set in a future Australia, where a cataclysmic event – known as The Collapse – has flung society to the wolves. There's no law, no system, no rules. It's at this point, says Pearce, that human behaviour gets interesting.

"In Hitler's bunker, when it was getting towards the end, they all started having sex with each other," he says. "When all of the things that keep us in check go, what's left?

"There's an underlying level of support we have for each other that we take for granted. The reality is that within three steps it could go wrong. Someone could come in and point a gun at me and you could go, 'Fuck you, I'm out of here.' Your fear kicks in, so your survival kicks in."

The post-Collapse world of The Rover is ruled by the trigger-happy. Pearce's character, Eric, has learned to survive by feeding on his fear. His family is dead. His home is in ruins. His car's been stolen. Hollowed out by grief, his only goal is to take violent, bloody revenge on the gang that stole his motor.

Pearce brings pedigree, but frankly, The Rover is a bit of a mutt. It's brutal and unsatisfying: Mad Max without the zaniness, A Fistful Of Dollars without the charm. Robert Pattinson plays Pearce's roadmate, a simple-minded American called Rey, and he's eager, but anxious in the role. He winds up lost in the wilderness.

But Pearce – as ever – is magnificent. He salvages the film in the same way he's rescued a clutch of duffers (The Time Machine, Lockout, Lawless) over the years. His Eric is patch-bald and flea-bitten. He stalks the outback in a ragged Steve Irwin get-up that would look ridiculous on a character less terrifying. It's an intense, sensitive performance of the type you can take for granted from Pearce. He is, once again, the soundest thing in a shaky movie.

Born in Ely, Cambridgeshire, in 1967, Pearce moved with his family to Australia aged three. His dad, a test pilot, was killed in a crash five years later ("Every time I get in a plane I think about what it would be like to have the pilot say, 'Sorry, we're plummeting to earth.' And you're done," Pearce says). After his dad's death, he was brought up by his mum, Anne, with his older sister, Tracey. The family lived in Geelong, Victoria, where a teen Pearce began acting and competing in body-building contests.

In 1986 he was cast in Neighbours after writing to Grundy Television to ask for a part. The buzz around his first major film role in 1994, as the fiery drag queen Felicia Jollygoodfellow in The Adventures of Priscilla, Queen Of The Desert, aroused the interest of Curtis Hanson, who cast him as sergeant Edmund J Exley in his 1997 adaptation of James Ellroy's LA Confidential. The nouveau-noir won two Oscars and pulled Pearce into a group of acting talent (Kevin Spacey, Philip Seymour Hoffman, Julianne Moore) that would come to define American indie cinema over the next decade.

Then, the pressure to keep working got to him. He made four films in quick succession before going on hiatus. He spent 2002 tucked up at home, playing guitar and smoking lots and lots of pot. He was, he's said an "all-day, every day" smoker.

"I really enjoyed being an actor as a kid," says Pearce of his wonky year. "I just had to work out, as a 30-year-old, am I still doing what I want to do? Acting's a pretty extreme process. It's not like I'm on the front line in Afghanistan, but emotionally it's pretty fucking full-on. I just learned to take better care of myself. I realised how important the break between jobs was. It's like when you put the weight down. You need that minute to allow the muscles to regroup."

The job that got him off the couch was The Proposition, another Australia-set western about murderous revenge. Pearce plays Charlie Burns, a convict in the 1880s outback who must kill his older brother in order to go free. Charlie is snivelling and treacherous, but alluring. Pearce had always been good at moral uncertainty (Memento, a pre-pot barnstormer in which Christopher Nolan cast him as a man with no short-term memory, wouldn't fly with a beef-stock hero in the mould of Russell Crowe), but after The Proposition he became more confident in how to toy with the audience's trust.

Since his comeback there's been a fierceness in Pearce, something fascinating and frightening about his sharp handsomeness. He is never the true hero, nor the out-and-out baddie. The muddle in the middle is where he finds the fun parts. Plus, he says, we have to stop taking our entertainment so easy.

"People say, 'Are you the good guy or the bad guy?'" he says. "You really need me to answer that question, huh? You're not going to cope if I say something in the middle, are you?

"Now, I get that the majority of people out there are more likely to pay to go and see Pretty Woman for the 12th time than they are to take a risk on The Rover, but I certainly wouldn't want things like this to become extinct. It's kind of sad to think that we can go down that road so easily. You get home, you're a bit tired, and you think, 'I'll just flick on something daft.' We're all inherently lazy, aren't we?

"I certainly think that it's possible for us to go down the more positive road, I just think it takes more of an effort. I'm probably more pessimistic than I am optimistic. Or maybe it's realism."

Perhaps that's why The Rover appealed to him: it's not clear cut. Eric isn't honourable or monstrous, he's just surviving in a society of people trying to do the same. The real-world parallels in Michôd's work are clear ("Kids are running around in certain countries with machine guns, The Collapse has occurred there already," says Pearce), yet, in fiction at least, life after the breakdown of everything is simple: you get by, even if it means stopping someone else from doing so. People become neither good, nor bad, but, just like that hotel lobby eagle, unpredictably wild.

The Rover is out in cinemas nationwide from Friday

• Peter Bradshaw's review of The Rover
• Watch the trailer for The Rover