Redmayne is playing Newt Scamander in the Harry Potter spin-off Fantastic Beasts and Where to Find Them, and according to the Rowling legend, Newt travelled the world in the 1920s writing an encyclopaedia of creatures that is now read by first-year students at Hogwarts.

"I met her once," Redmayne whispers. "It was when her and David Yates were working on the script ... and it was meant to be a meet-and-greet and a wee chat. I got a sense that her time is so precious, so we ended up getting right down to the root of who Newt is. Her mind is so alive – it was a real pleasure. It was in one of these rooms, about 30 metres away."

We are in an office building on the Fantastic Beasts set at Leavesden Studio, just north of London, and the studio has been dressed to look like prohibition-era New York, where the action takes place over three days in December 1926. Redmayne is wearing the white shirt that will soon become part of the iconic look of his Newton Artemis Fido "Newt" Scamander.

The actor, 34, says working with Rowling is fulfilling a dream. Redmayne was 15 when the first Harry Potter book came out in England. A few years later, while studying art history at Cambridge University, "I was dreaming of getting an audition for the films," he says. "There was this moment where it seemed that every English actor was getting the opportunity, particularly if you had reddish-brown hair. While at university, I did audition for the part of Tom Riddle. I didn't get it."

Riddle grows up to be Voldemort, and it's impossible to imagine Redmayne in that role. He seems too nice and awkward to play the most evil being in the world. Redmayne has an embarrassing shyness that makes him modest and self-deprecating when talking about his own successes. He was apologetic when he first met Fantastic Beasts director David Yates.

"For five or six years I've had this battered old Globe-Trotter case that I use to put all the things that I need when I go on set," says Redmayne, who went to the boys' school Eton College just outside London alongside the likes of Prince William. "When I first met David, we went to have a coffee and he started telling me about Newt and that he had a magical brown leather suitcase. I quickly told him: 'I didn't come here with a case to be Method [acting] or show off. I had no idea'."

Yates quickly saw character traits he wanted to play the socially awkward Newt. "Eddie had got an amazing combination of fragility and strength, and depth, and he's funny. That is a wonderful combination for Newt Scamander. And he's slightly – and I hope he forgives me for saying this – he's obsessed with detail, so when he prepares for a scene, he needs to know the minutiae of everything, and that is very Newt."

Redmayne researches his roles extensively. For his 2015 Oscar-winning turn as Stephen Hawking in The Theory of Everything, he spent several months at a neurology clinic in London, working with a specialist and meeting the family of victims with similar conditions. He was as thorough in his research of Newt, doing his best to find real-life situations that would enable him to play a "magizoologist", which in the Potterverse is someone who studies magical creatures. Newt is more comfortable with animals than humans.

"What was fun for me is: how do you approach a character like that?" Redmayne says. He was nervous – "because it was the first time in a while that I had played a character who was entirely fictional". This was part of the reason he spent nearly all of his one meeting with Rowling asking her about the character's background: "It was the fear of really getting to grips with what her vision of Newt is."

Redmayne also got to meet a man he'd become fascinated by on YouTube. "I used it as an excuse to meet Damian Aspinall. He grew up with this young gorilla that is released in the wild. Five years later, Aspinall goes to find the gorilla, and when the gorilla sees him, he gives him a huge hug. It's mesmeric."

So Redmayne went off to Howletts Wild Animal Park in Kent, England, owned by Aspinall, to meet the people who look after the animals. He would watch as they entered the area for big cats and interacted with tigers, paying particular attention to their sounds. He also went on a tracking course in a British forest, hearing about how different plants could be used as remedies.

"The way I move in the film is interesting," says Redmayne, who jumps off his seat to demonstrate. "If you're tracking animals, you have to have an open gait because, if you're going to step on a twig, then in order to crunch it without making too much noise you have to put all your weight on your feet like this."

As he did for playing Stephen Hawking and The Danish Girl's Lili Elbe, Redmayne used choreographer Alex Reynolds to help define his movement. "My fear for the film, because so much is imagined, and so much will happen in post-production, is that you don't have enough information [to make Newt seem real]." Not wanting to leave anything to chance, Redmayne asked the director to allow him on the film set during preparations and let him see the artwork concepts of the fantastic beasts, as well as talk to the animators.

Redmayne received his first acting credit aged 16 in the television show Animal Ark. A wry smile appears as he describes how his affinity to animals was lessened somewhat by an experience on set. "The character I was playing is supposed to be a dog lover and for one scene, the dog handler put liver pate on the back of my ear, so when I opened the door, this dog would come over and lick it all over my face. Every time the cameras would roll, I would have to take a deep breath."

Now that Redmayne has a wife, a child and an Oscar, he can more easily laugh off some of the roles he took during his rise. Redmayne married long-time partner Hannah Bagshawe, a public relations executive, in December 2014. In May, they had their first child, Iris. For Fantastic Beasts – the first of five films planned in the franchise – the couple's discussions on living arrangements and time away from home during filming became easier when Redmayne was told filming would take place in a studio, rather than on location.

Winning an Academy Award can make going out in public more difficult, yet the low-key Redmayne still takes the subway around London. He says winning the Oscar has not really changed how people view him. "I don't think people [show me more respect]. I don't really notice."

Fantastic Beasts and Where to Find Them opens in cinemas on November 17.

Animal logic: a great eight

Eddie Redmayne's Newt Scamander has an affinity for fantastic beasts, and he's not alone in cinema. Here are eight memorable movies with characters who communicate with animals:

Dr Doolittle 
Rex Harrison plays an eccentric doctor with an ability to speak to animals in this 1967 musical comedy. The film was remade in 1998 with Eddie Murphy in the titular role and spawned several increasingly barking sequels.

Grizzly Man 
Werner Herzog's extraordinary 2005 documentary uses archive footage shot by amateur grizzly bear expert Timothy Treadwell, who journeyed to Alaska to study and live with bears.

Jungle Book 
There have been several films inspired by the Rudyard Kipling book, but the one that still stands out is the 1967 Disney cartoon – the last animation Walt Disney directly worked on. In it, Mowgli learn about the bear necessities of life.

Crocodile Dundee 
In the 1986 comedy, Mick Dundee uses the power of hypnosis to put a water buffalo to sleep on a road, so that he can safely drive by the animal. His methods are more professional than the dog-biscuit-eating Martin Riggs in 1987's Lethal Weapon.

Three Amigos 
In John Landis' classic 1986 comedy, Steve Martin, Martin Short and Chevy Chase start to sing Blue Shadows, written for the film by Randy Newman, and their horses and other animals join in.

Every Which Way But Loose
In an unusual comic role, Clint Eastwood plays a trucker and brawler travelling across the American West in search of a country singer he's smitten by, alongside his pet orangutang, Clyde.

The Wizard of Oz 
Far from Kansas, on the yellow brick road, Dorothy meets a cowardly lion without a heart. Yes, we know: it's a man (Bert Lahr) inside the costume.

Tarzan
He's the lord of the jungle and even talked to the animals when he appeared in silent films. The most famous screen incarnation of Tarzan was by Olympic gold medallist Johnny Weissmuller, who played the character in 12 films before they fell out of favour in the 1970s because of their sexist and racist stereotypes.