For an actress who first made her mark in Trainspottting as a schoolgirl doing things with junkie Ewan McGregor that her slumbering parents would surely have disapproved of, Kelly Macdonald admits she was a bit of a failure at being a teen rebel.

“I didn’t have much to rebel against,” she says.

She is certainly nowhere near as willful or energetic as the tomboyish Princess Merida, the character she voices in Disney-Pixar’s new animated feature, Brave.

“The description of Merida is so far removed from me that if it was a live action I think I wouldn’t have been in the casting room.

“I’m far too old, I’m not physical or athletic or beautiful enough, so thank goodness it’s an animated version.”

What she found less difficult was snapping back into a teenage mindset.

“The teenage aspect wasn’t a challenge. I am ashamed to say that came back really quickly, even after 17 years.

“I just had to pretend my mum was in the room. Nothing winds you up like your parents.”

Kelly, 36, has firmly established her career in Hollywood, starring in Emmy Award-winning series Boardwalk Empire and Oscar winning films such as No Country For Old Men.

Born in Glasgow, being in Brave means she was able to return to Scottish roots for her voice acting debut.

The film, which opened this week, is set in the mythical medieval Scottish Highlands and Kelly leads a predominantly Scottish cast including Billy Connolly, Kevin McKidd and Robbie Coltrane.

Oscar-winning actress Reese Witherspoon was originally in the frame to play Merida and had already recorded some lines before dropping out due to scheduling conflicts, at which point Kelly stepped in.

“It was an amazing experience and one I never thought I’d get the chance to do. I feel very privileged,” she says.

“I was totally blown away when I saw Merida for the first time.

“I just couldn’t believe what Disney-Pixar were capable of.”

Merida is Pixar’s first heroine, the flame haired and fiery, horse back riding, bow and arrow shooting daughter of King Fergus (voiced by Connolly) and Queen Elinor (Emma Thompson).

“I feel quite proud to be the voice of Pixar’s first female protagonist,” admits Kelly.

Merida’s parents are intent on marrying off their daughter to the first-born son of one of the other clans, but the feisty teenager runs off, crossing paths with a witch (Julie Walters) whom she begs for help to change her fate.

Kelly amended some of Merida’s American-written lines, adding some Scottish colloquialisms, but the biggest challenge lay in just using her voice to act.

“I’m the queen of subtlety when I’m working, but you can’t rely on any facial movements so it was really difficult for me. I always underplay everything but you can’t get away with that in animation.

“It was a real learning curve. In the end, it was really liberating and I was just enjoying myself.”

Kelly – who has a four-year-old son, Freddie, with her husband, Travis bassist Dougie Payne, and is expecting the couple’s second child – is thrilled with what the film stands for.

“Being a mother myself, the big message of Brave is brilliant – a mother makes some mistakes and apologises for them,” she says.

Kelly has come a long way since Danny Boyle selected her at the age of 19 to play precocious schoolgirl Diane Coulston, despite her lack of formal acting training.

Since her big-screen debut, which received a Bafta Scotland nomination for Best Actress, the former barmaid has starred in films including Elizabeth, Gosford Park and Harry Potter And The Deathly Hallows – Part 2, not to mention her acclaimed role as Margaret Schroeder in Prohibition-era drama Boardwalk Empire.

She next appears in Joe Wright’s Anna Karenina, alongside Keira Knightley, Aaron Johnson and Jude Law.

Thanks to her success across the pond, she now splits her time between her flat in New York – where Boardwalk Empire is filmed – and her Glasgow home.

Boardwalk Empire is set to return for the third season in the autumn, but if she knows anything about what is in store for Margaret, Macdonald is keeping quiet.

“I can’t give anything away but things don’t start well, I know that much. We’re halfway through season three and it’s not happy families.”

She is hoping that Scorsese, who sat in the director’s chair for the pilot, will return to direct another episode.

“There are always rumours flying around that he’s going to direct another episode but it’s not happened yet. It would be amazing.”

* Brave has opened this week and Anna Karenina opens in cinemas on Friday, September 7.