It's a bright, crunchy winter morning and Ben Mendelsohn wants to walk while we talk. More than that, he wants to smoke. Would you like to try disagreeing with Ben Mendelsohn? Me neither. So we walk. The narrow Soho streets are sticky with last night's beer and crammed with people. Within seconds, the 44-year-old Australian actor is a few steps ahead and I have to strain to catch his words, which isn't as tricky as it sounds since most of them are "fuck".

"People are never shy about telling you what they fucking think," he calls back at me through the crowd. "At the same time, fuck that. Fuck what they think they fucking want or this or that or fucking any of it." I worry that I've lost the gist. I had asked if he knew why people cast him: what they see in him, what they want. So is he talking about directors? "Nah, just fucking everyone." Ah. Good to have cleared that up.

I steer him towards a park, where we pick out a bench and sit huddled against the cold. Up close, almost cheek to cheek, he is handsome, sinewy, and a little rodent-like: his shaggy, sandy-coloured hair is threaded with grey, and there is blond in his eyelashes and eyebrows. Faint freckles have been scattered across his tanned face. He's wearing jeans, deck shoes, a plaid shirt and a rustling navy waterproof. Even though we're seated, with a toddler in a rainbow cardigan twirling dizzily nearby, he is full of jittery vitality: he shifts in his seat, jiggles his feet, glances around. Eye contact is occasional but intense. When I email the photographer later to see how the shoot went, she replies: "He was nice and very friendly but annoyingly wriggly, a bit like a toddler."

But then a laidback Ben Mendelsohn would feel all wrong, like a Christian Bale who couldn't be arsed to lose weight for a part. We've rarely seen Mendelsohn play nice on screen. Not in Animal Kingdom, his 2010 break-out film, in which he played the ferrety psychopath Pope; or 2012's Killing Them Softly, where he was a smack-addicted hood. Even at 17, the die was cast: he won an Australian Film Institute award for playing a delinquent with an Elvis sneer in The Year My Voice Broke. In Starred Up, the new prison drama we have met to discuss, he has wrenching moments of sensitivity and hurt as Nev, a convict whose son – played by Jack O'Connell – is thrown into the same prison as him. The closest we've come to a Zen Ben was in The Place Beyond the Pines, in which he was Ryan Gosling's motorcycle-riding mentor-in-crime.

"Probably the best week of work I ever had," he says of Pines, grinding his cigarette butt into the concrete, then sparking up again. "My character got flipped from being a puppeteer kinda guy to someone who wanted to be besties with Ryan. That took us all by surprise. So Ryan and I weren't going in like, 'I'm the toughest guy that ever lived!' 'No, I'm the toughest guy that ever lived. Grrr!'" He has just finished working on Gosling's directorial debut, How to Catch a Monster, of which he will only say: "Ryan's beautiful. He's off, cutting away, doing what he's doing. If he uses some of the stuff I think he's gonna use, then we'll really have some…" He trails off.

As for Starred Up, he has no idea if it's any good because he doesn't watch his own work. He can tell me what it was like to make though. "Fucking horrible. Horrible. One of the shittiest fucking shoots I've ever been on. It was very rushed. They were trying to shoot a lot in a short time. We were in a prison, it was freezing. I didn't like it. But that doesn't matter. Who gives a shit? Most of the ones that end up being all right are a fucking pain in the arse. Most of them. There was a bit of rehearsal. Talky-talky. That stuff is overwrought, for my money. When the cameras roll, that's the real deal."

The most striking aspect of Nev is that he is a straight man in a loving relationship with another convict. "I've known plenty of guys that have been in prison," he says. "Some of them talk about that side of it more than others do but, you know, durrr." He lights another cigarette, then says thoughtfully: "They were gonna take that out." Who are "they"? He looks at me blankly. "Whatever. It was gonna be taken out. All that stuff was gonna be gone. I heard that and I was like, 'Why would you do that?' I thought that was a very bad idea for a number of reasons. So it stayed in." Because of you? "Well, I don't know. Let's not, I won't … Look, they thought they didn't wanna go there. But they sensibly rethought their options."

Jack O'Connell and Ben Mendelsohn in Starred Up.

Mendelsohn is obviously someone who can frame his argument persuasively. He insisted on ironing out every wrinkle in the screenplay of Animal Kingdom ("They were trying to describe a fantasy about people rather than something I could play, and that might be my own failing but I don't fucking think so") and on keeping his distance, on set, from the young actor who played his nephew. "I didn't want him to get all chummy-chummy, all that bullshit. That wasn't my idea: I stole that from fucking Terry Malick. He kept Colin Farrell and Q'orianka Kilcher apart before their first scene on The New World." I didn't know that, I say. "Of course you fucking didn't! Nobody knew that."

Mendelsohn's casual mention of Malick gives a fair indication of how his fortunes have improved in recent years. As well as The New World, he's starred in The Dark Knight Rises, Killer Elite alongside Robert De Niro ("The only guy I was ever interested in thieving from when I was starting out"), and in Baz Luhrmann's Australia. The work keeps rolling in. "I'm in a very lucky period," says the actor, who is married to the British writer and journalist Emma Forrest, with whom he has a 10-month-old daughter. "They like it at the moment. They don't always. The thing about acting is you have to wait to be asked to the dance. I'm fairly confident now they'll keep asking."

His memories of the bad times are still close to the surface. As we walk back through Soho, he rattles off an impatient precis: "The very rough story is this: Melbourne boy, out of both my parents' houses at a young age, lived with my grandmother, drama teacher twisted me into doing this TV thing that I thought my mates were doing too. They didn't, I did. Fifteen years old, out in the world, acting was all I had. It had a family-type environment, a bit of kudos, a successful period in my late teens, early 20s, the golden child and all that, but nothing was guaranteed, there were two years when I barely did a fucking thing."

The words "golden child" are spat out. "Oh, I hated that. Fucking hated it. After The Year My Voice Broke, I got very uncomfortable. I still had a merit-based idea of things and I didn't feel I was ready or good enough. I didn't like the degree of attention. I'm very cagey by nature."

He's proud of his stint on Neighbours in the Kylie-and-Jason years. "It's a fucking behemoth is what it is!" he says. "Ramsay Street deserves respect." He is more suspicious of acting in general, though. As we round our final corner, he says: "All I see most of the time is mistakes. You see the way actors will fuck up a scene trying to be above it or beyond it and I fucking hate that too-cool-for-school shit. It's why kids generally wipe the floor with any adult actor, and why dogs are so incredibly watchable. Dogs and cats. I could watch them for ever."

• Starred Up is out on 21 March