The big-budget series, created by Terence Winter, who wrote The Sopranos, and directed by Martin Scorsese, is already a huge hit in the US and looks likely to win an army of devoted fans over here. Set in Atlantic City at the end of the First World War, the glossy HBO drama revolves around Enoch "Nucky" Thompson, New Jersey political boss and racketeer, played by Steve Buscemi, and his cohorts. Macdonald plays Margaret Schroeder, an Irish immigrant with a violent husband, who strikes up an unlikely alliance with the nefarious Nucky after she hears him speak at the Women's Temperance League.
It's a lavish show - the pilot episode reputedly cost $20 million, making it the most expensive in US television history - but investors are reaping the rewards. Boardwalk Empire won best dramatic series at the Golden Globes, although Macdonald lost out as best supporting actress to Glee's Jane Lynch, and the cast scooped the best ensemble performance at the Screen Actors' Guild Awards. The show is also nominated as best drama and best new drama in this weekend's Writers' Guild Awards.
Her role has turned Macdonald, 34, into the most talked about British actress in the US, but she prefers to ignore the maelstrom of attention. She loves the show and admires her co-stars but casually admits that she can't remember if she signed up to play Margaret for four years or six. "Six? I think it might be four. Four or six. I don't know. It's all unknown. I could be killed off," she said.
Similarly, she had no idea such vast sums of money were being spent on Boardwalk Empire, so she never felt the same pressure as some of the cast and crew. "I never know the ins and outs," she said. "I meet a series of producers and never quite know who anybody is. I often wonder if I should pay more attention."
She adopted the same breezy approach when offered the role. She agreed in principle after hearing that Scorsese was directing, and signed up on the back of a transatlantic telephone conversation with Winter. There was no audition. Her only lingering concern was that Winter mistook her Scottish burr for an Irish brogue and gave her the role thinking she hailed from the same country as her character. "They didn't pick up on it," she said. "I think some people thought I was Irish. Don't tell them I'm Scottish."
Macdonald's apparent lack of drive in one of the world's most competitive industries has served her well. She won her first acting role in Trainspotting alongside Ewan McGregor after picking up a flyer in a bar that asked "Do you want to be the next Sharon Stone?" It could have been a one-off job for the teenage waitress who was thinking about going to art school, but instead Macdonald became one of the most sought after actresses of her generation.
Those who know her insist it hasn't all been a happy accident. Macdonald is petite, softly spoken and resolutely unshowy, but behind her meek exterior lies a steely determination to succeed. She has worked hard to get where she is.
Kelly Macdonald was born and grew up on the South Side of Glasgow. Her parents, Archie and Patsy, divorced when she was 14 and Macdonald went with her mother and younger brother to live on a council estate in Newton Mearns. She fell out with her father around that time and the two are no longer in contact. A few years ago her father gave an interview to a tabloid, blaming their estrangement on Macdonald's celebrity, but his daughter has always refused to speak about him.
Macdonald had no career plan when she left school aged 16, and was working as a waitress when she spotted the invitation to an open casting session for Trainspotting. The director, Danny Boyle, said later that he knew Macdonald would win the part of Diane as soon as he laid eyes on the shy brunette teenager. "We narrowed it down from ten to six to two, but it was Kelly all the way," he said. "She has that thing Ewan McGregor has: indefinable star quality, yet they're ordinary people. There's something about them that connects with people. Ordinary but extraordinary."
The film's success prompted Macdonald to move to London but she struggled to find challenging roles. Prolonged periods of unemployment gave way to roles in low-key films. It was an opportunity for Macdonald to work with more experienced actors and directors and hone her craft.
But Macdonald believes it was her small part in No Country For Old Men that was her breakthrough role. She played Carla Jean Moss, the Texan wife of the film's protagonist, against the advice of her agent who thought she wasn't right for it. Her determination paid off and gave her the opportunity to work with the Coen brothers and co-star Josh Brolin. "It was one of the best experiences of my working life," she said. "It was just so easy."
Away from the studio, Macdonald lives in a 1 million house in Glasgow with her husband Dougie Payne, the bass player in Travis, and their two-year-old son Freddie. The couple met in 2000 through mutual friends and married in 2003. They moved back to Glasgow from London last summer to be nearer their families, and split their time between Scotland and New York, where Boardwalk Empire is filmed.
Macdonald is now back in New York beginning work on the second season of the hit show. She says she likes the security of knowing what she is doing for at least the next year. "I don't have to think about it," she says. "I have a private life, a life outside of acting. If I was a young single person I might want to be working constantly, but that's not what I'm after."
At some stage she is going to have to see herself on television to understand what the current buzz is about, but she isn't keen. "I don't think it would be helpful to me to watch while I'm still doing the show," she said. "I might watch it when it's all over and done with."
Facts of Life
• To prepare for her role as an Irish immigrant in Boardwalk Empire, Macdonald read Sister Carrie by Theodore Dreiser, a 1900 novel about a country girl moving to the city in pursuit of the American dream.
• Macdonald grew up ten minutes walk from her future husband, Dougie Payne, in Glasgow, although the two didn't meet until 2000.
• In Some Voices, Macdonald shared a bath with James Bond actor Daniel Craig, above.
• Macdonald has yet to tell her Boardwalk Empire boss, Terence Winters, that she has never seen his legendary TV show, The Sopranos.
• Boardwalk Empire is the second time Macdonald has had to use an Irish accent - in Intermission she played a character from Dublin and Margaret Schroeder is from Kerry.
• Among the parts Macdonald didn't get were Gwyneth Paltrow's role in Shakespeare In Love and Nicole Kidman's in Moulin Rouge!