HE made a romantic hero out of a rubbish-collecting robot in Wall.E, had audiences crying oceans over a lost fish in Finding Nemo, and in his new film John Carter he puts a Confederate soldier on Mars.

But the toughest thing computer animation pioneer Andrew Stanton has had to do lately? Pass the shop-worker test.

"I'd been sitting down making movies for 20 years and suddenly I was standing up all day for 100 days straight," he says of filming John Carter. "Didn't matter whether we were inside, outside, cold, hot. That was insane. I was amazed I muscled through it."

Based on the Edgar Rice Burroughs novel A Princess of Mars, the Disney tale of a stranger in a strange land is Stanton's first live action film. It is also a very expensive one. As happened with James Cameron's Avatar, no-one is saying exactly how much the final film has cost, leaving guesstimates to settle at upwards of $250 million. Stanton has said he was on budget – estimated to be $175m – and on time, during the shoot.

With Finding Nemo bringing in $868m worldwide and Wall.E $521m, Stanton has shown he can pay the bills. Whether he can deliver similar profit margins with a live action family film at a time when family finances are tighter than ever, is what the industry is waiting to see.

Among science fiction aficionados, Rice Burroughs's John Carter is the sun and the moon and the stars. Credited with inspiring everything from Star Wars to Avatar, writers from Arthur C Clarke to Ray Bradbury, Stanton first discovered the book at the age of 10 and was desperate to one day see it on the screen. As for who might get it there, the young Stanton didn't think it would be him.

"I never had the hubris to think I'd be in film or directing, let alone doing this film," he says when we meet in London.

That he should end up doing so with Disney is a tale straight out of a Disney writer's imagination. Once upon a time there was a young man by the name of Andrew Stanton who went for a job with Disney. He was turned down. Then turned down again. And again. So he went off to join this new kid on the block outfit called Pixar. That worked out so well he returned to Disney years later to direct one of its biggest releases this year.

"Absolutely," he says when I ask if being rejected by Disney all those years ago was the best thing that could have happened to him. "I was going to be very happy to be hired by Disney and just be an animator or a clean-up artist." Instead, he taught himself how to write movies, direct them and became a key player in films that have raised the bar for animation to just below cloud level. As he puts it: "It's all been gravy since the first day I walked into Pixar."

Which makes one wonder why the 46-year-old would want to leave that computer and desk chair behind and make live action. Isn't that giving up being master of all you survey?

"That's more people's assumption of what it must be like to be working in computer graphics. It's actually the most unwieldy, unforgiving toddler tool in the world, it will not co-operate and it takes a massive army of people to fight at it and get it to just do something really simple half the time. If you knew how many times we've said I wish I could be outside and just shoot it, just do it, and it would be done."

Brought up in a fishing village north of Boston, Stanton always wanted to do something in entertainment, but whether that was acting, music or drawing, he wasn't sure until he found out, at the age of 16, about the California Institute of the Arts, the school founded by Walt Disney. After that, he says, he was like the Richard Dreyfuss character in Close Encounters of the Third Kind – he had to get to this fabled site.

Like many a Pixar person, there's something about Stanton that makes him seem forever young, endlessly boyish. When he talks about buying scripts in the early days and studying them to see what worked, his is the wide-eyed fervour of the young model aeroplane maker, or the kid who has seen Star Wars for the first time. Saucer-eyed syndrome, one might call it. He gets the same gleeful look when talking about going to rock concerts (the last one was Roger Waters of Pink Floyd).

There was a lot of saucer-eyed syndrome about when he joined Pixar in 1990. At that point the team was just nine people. "We were all crammed in the same office half the time, timesharing computers and sharing one phone in the centre of the floor. When it rang we all ran for it. Fighting over what CD got played in the stereo. It was very dorm living."

Then there was the boss, one Steve Jobs, who told them to trust their instincts, to lead and never follow. If there is such a thing as a secret to Pixar's success, he says, it is not one that people want to hear because there's nothing easy about doing it.

"We've created an environment where you try to be wrong as fast as you can, where you have to make mistakes and you have to make them as big and as early as you can so that you can learn the maximum amount and then pick up the pieces and try it again."

He explains: "It's a very humbling, scary environment to be in. It's all very supportive, but it's not for the weak. It's like being part of an Olympic team, you all have to be on your A game just working your hardest." So not all sitting round on beanbags and eating jellybeans, then.

Stanton's two Oscars were for Finding Nemo and Wall-E. The father of two, married for 31 years, calls the former "completely personal" and the latter, about two robots falling for each other, "the most pure love story I could think of". Besides his family and work, the other constant in Stanton's life is his faith. It is something he likes to keep private, and doesn't think it has any bearing on his work.

"I think any values that I have come through, but I like to think most values I have aren't driven by an organised religion, they're driven just by being a humanitarian. I've never wanted to be preached at, nor do I want to preach to."

With his first live action film behind him he's felt the fear, done it anyway, and now waits to see how the movie will be received. He says he'd do live action again if that's what the story called for.

I ask him how many story ideas are percolating in his head at the moment. "At least eight," he laughs, eyes widening in anticipation.

"It's just whether I'll get them done before I get too old."

John Carter opens in cinemas tomorrow