Even by the usual standards of the Isle of Skye in early February, it wasn't the balmiest of mornings. Visibility was so poor that Marion Cotillard, one of the two stars of the new cinema adaptation of William Shakespeare's Macbeth that was filming on the island, had strayed into a bog and disappeared from view. It had taken two crew members to fish her out while the mud sucked at her feet.

By midmorning, the temperature was still 10 degrees below freezing, and the hail was so furious that the director, Justin Kurzel, had to fasten industrial fans to the fronts of his cameras to blow it out of shot. After calling action, Kurzel and his crew watched scenes on a monitor under a flapping tarpaulin. But Michael Fassbender, who was playing Macbeth, had to stand there unshielded, his face turned towards the storm.

I meet Fassbender 15 months later, on a roof-terrace bar during the Cannes Film Festival, the day before Macbeth's world premiere. It's 29C outside, and the sun gleams over the bay like a polished plate. The 38-year-old actor is sitting with his shirt unbuttoned to the chest, and his teeth are bared in a wide, wolfish grin.

The terrace is preposterously out of whack with the on-set conditions Fassbender is describing, and we're both laughing semi-guiltily at the contrast. He concedes that the weather during the Macbeth shoot was on occasion "restrictive". But for Fassbender, restrictive is good.

"Innovation comes through restriction," he says. "And while on a big film you've got all the options in the world open to you, on a small film even getting it made is a hard thing. I love how fast you have to work – that pressure of having to get it right in one take or not at all."

Whether the budget allows for one take or 50, Fassbender's capacity for getting it right is now well known. It's almost impossible to leave one of his films without feeling you've just seen one of the greatest actors of his generation swinging away at the coalface.

His first major screen role came in 2001, with a part in the HBO series Band of Brothers. But his real breakthrough came seven years later with Steve McQueen's Bafta and Cannes-winning Hunger, in which Fassbender played the IRA hunger-striker Bobby Sands, and survived on water and seeds to lose more than two stones for the part.

He went on to star in two more films for McQueen, Shame and 12 Years a Slave, as well as playing the villainous Magneto in two X-Men films (a third is due next summer), the luxuriantly named Lt Archie Hicox in Quentin Tarantino's Inglourious Basterds, David, the T?E Lawrence-channelling android in Ridley Scott's Prometheus, a thunderous Rochester in Cary Fukunaga’s Jane Eyre, and other unquiet souls.

Looming on the horizon, too, is his Steve Jobs biopic, which had its world premiere earlier this month. Fassbender’s performance as the uncompromising Apple CEO was widely praised, and is expected to put him in serious contention for a best actor Oscar next year.

One particular line kept popping up in the Steve Jobs reviews, which is hissed by Jobs at the height of his paranoia and egomania. "I'm like Julius Caesar. I'm surrounded by enemies." Fassbender does his best work alone, at the edge of the world, and never more than a few footsteps from tragedy.

Which brings us back, of course, to Macbeth. Fassbender hasn't seen the film when we speak – he wanted to save his first time for the premiere – and admits he’d never previously considered playing Shakespeare, either on stage or on film, until this particular opportunity reared its head.

"I'm not the type to say, 'I always wanted to play the Dane,'?" he drawls, his voice dropping into an unexpectedly hilarious impression of Withnail and I's Uncle Monty. (Discovering Fassbender can be funny is a shock on a par with discovering a crocodile can yodel.)

He remembers studying Macbeth at secondary school in Killarney, County Kerry, where his family relocated from the German city of Heidelberg when he was two years old. (His father’s side of the family are German; his mother's from County Antrim.) He found Shakespeare's words "alien... but it was no wonder, because we read it like a novel, and it's supposed to be on its feet.” What changed his opinion? “I think every actor should do it once. And the opportunity to have a go is a great privilege, even though I was s------- it.”

Fassbender's decision to play Macbeth was the keystone the producers needed to hold the rest of the project up. He joined the film in early 2013, and Kurzel quickly followed as director. Fassbender loved Kurzel's first film, the forbidding crime thriller Snowtown, and also his vision for the Macbeth character. The Australian filmmaker had imagined the ruthless Thane as a general suffering from post-traumatic stress disorder, literally haunted by his previous experiences on the field of battle.

"When Justin said it, it was so obvious," Fassbender enthuses. "Because it's actually in the play, in the banquet sequences – Lady Macbeth tells everyone to relax because she’s seen this behaviour before, he's prone to fits. He's seeing Banquo and the witches in the same way that soldiers coming back from Iraq can be walking through Clapham Junction and next thing they’re in downtown Basra.”

Until his own film was safely finished, Kurzel avoided watching the three most highly acclaimed existing screen Macbeths by Welles, Kurosawa and Polanski: "I didn't fancy making this with Orson Welles hanging over my head, no," the director tells me later, with a dark laugh. But Fassbender sought out and pored over all three.

Why put himself through that? "It's information that's out there, and it can only lend something to what I'm doing," he shrugs. Fassbender does not make things easy for himself: he’s known to spend weeks labouring over scripts, experimenting with nuance and inflection on every line, until he lands on the best possible way of delivering it.

Unsurprisingly, then, he's a self-confessed "slow learner” when it comes to memorising dialogue. A recent spell on the set of Terrence Malick's as-yet-untitled romantic drama was terrifying, he says: Malick “handed me 80 pages of script when I arrived on set on the Wednesday, and we were filming on the Friday".

He recalls a panicky late-night phone call with the director, in which Fassbender brokenly confessed that "the best he could do" was commit a few pages to memory and improvise the rest. “And he said, 'You know, Michael'?" – Fassbender does an uncanny impression of Malick’s fluting Texan countertenor – "?'this is Starbucks-induced dialogue. I’m sure you’ll do a much better job of interpreting it yourself. Do you like dogs?’?” Then they spoke about dogs for a bit, and that was that.

When films go wrong, they haunt him. When our conversation moves on to The Counsellor – a nihilistic, Cormac McCarthy-scripted thriller from Ridley Scott that got murderously bad reviews – he talks about it in a way that suggests the whole thing was entirely his fault. (It really wasn't.)

He got "a lot of things" wrong in his performance, he says, with a visible wince. "I love working with Ridley. But I just didn't – I'm not happy with a lot of things I did."

Did the surreal bleakness of McCarthy's screenplay – it involves multiple head-chippings and finger-loppings and Cameron Diaz having sex with a car windscreen – throw the cast off-balance?

"No, we all knew what was going on. I just didn't think I delivered, you know?" When did he last think he delivered? “I never think that.”

A recent source of considerable pride, though, is 12 Years a Slave, in which he played the depraved plantation owner Edwin Epps: a performance that earned him his first Oscar nomination last year, for Best Supporting Actor. He remembers calling McQueen after reading the script and “begging to be a part of it, whatever that part was – whether it was just a day or two on set”.

He hoped that McQueen would cast him as Epps, whose dealings with both Chiwetel Ejiofor's Solomon Northup and his "favoured" slave girl Patsy, played by Lupita Nyong’o, have a savagery and horror that's hard to think about, let alone watch. Why hope for a role as contemptible as that? What was in it for him?

"Somebody's got to play the bad guy," he says. "And somebody's got to play the bad guy humanly. I like the idea that we're all capable of great things and terrible things. We shouldn’t keep them at arm's length."

He goes on, saying that he didn't want to see Epps "sectioned off" as a "pantomime villain": "It's more uncomfortable when the elements aren’t clear-cut. So I knew that I could do that, and that I could help tell Solomon's story.”

Did the responsibility feel like a moral one? "It always scares me when we start talking about morality," he says, looking a little rattled. “I think we’re living in such a morally judgmental world. No, it was just a priority for me to do it correctly.

"I mean, there's an element of Epps in everyone. When you talk about slavery, white people say ‘Well, I wouldn’t have been a slave-owner', and black people say ‘Well, I would have taken over the house, or run.'?" So why didn't they? "Survival is survival."

Perhaps that desire to see the best and worst of humanity up close is what made the teenage Fassbender consider a career in war journalism (he also fancied law, but couldn’t manage the paperwork). But when he went to an acting workshop at the age of 17, he knew he'd found his niche. He got his first professional gig when he was 18, in a stage production of Reservoir Dogs in his home town (he played Mr Pink).

After that came two thirds of an acting degree at Drama Centre London (he dropped out midway through year three after getting an agent) – and, following his big-break-that-wasn’t in Band of Brothers, six busy but mostly fruitless years on the Los Angeles audition circuit. Then in 2008, Hunger made him a star, and by October of that year, he was filming with Tarantino, in the country of his birth. Professionally and geographically, the circles were complete.

Next comes something of a Macbeth reunion. With Kurzel directing and Cotillard co-starring, he'll appear in the forthcoming Assassin's Creed blockbuster, which started filming in Malta last week. I ask how he thinks he'll adapt to the glamour of a Hollywood production after battling through hailstorms in the Hebridean wilds. His wolfish grin suddenly grows wider, and I'm momentarily seized by the ludicrous thought that he might be about to eat me up in a single bite.

"Well," he says, "we all need a release valve, you know?"