BEVERLY HILLS, Calif. — Actress Kelly Macdonald believes in fate. She probably should. Because at 20, without any training, she hustled off to an audition for the movie “Trainspotting.”

“I went along to that just to kind of build some confidence a little bit, so I knew what an audition felt like. And my next step was going to be drama school. And then I got the part, and drama school sort of fell by the wayside,” she said.

“For years I kept thinking, ‘Oh, everyone else has been to drama school, I have to attend. But I’ve got enough under my belt now, learning on the job. Often people don’t study what ends up being their career, what they love. People find their ways into different businesses, so we should rest easy and not give ourselves a hard time.”

For years she gave herself a bad time. “But I was quite shy and didn’t have a lot of confidence. I think the confidence thing was the real issue,” she said.

It’s no longer an issue for the 34-year-old actress. In fact, she co-stars in HBO’s impressive series, “Boardwalk Empire,” premiering Sunday. When she got the call to play a young Irish wife, Macdonald — who is Scottish — again counted on fate.

“My agent said it was written by Terence Winter, who was one of the head writers on ‘The Sopranos,’ and Martin Scorsese is producer. And he’ll direct the pilot. Already you know you’re going to HAVE to do it. I’m doing it whether it’s the worst script ever, or working with the most awful people ever, you’ve no choice at that point. I knew nothing about the character. ‘OK, that’s fine.’ ”

It is fine. One never suspects that Macdonald isn’t Irish to the bone or that she’s not the innocent wife who is beguiled by Atlantic City’s gentleman gangster.

Macdonald is best known in the United States for her roles in “Gosford Park” and “No Country for Old Men.”

“‘Gosford Park’ felt like I went up a little on the career ladder,” she said.

“It felt like I’d been promoted. Just within the industry, things changed a little bit for me because my performance is pretty subtle, and I think you have to really chew the furniture for the phone to start ringing off the hook and everything. And it wasn’t that. I certainly felt, within the industry, I went up a notch. It was probably after ‘No Country for Old Men’ that there were more offers.”

Acting had always been her dream. “Since I was really tiny it’s just been the thing I was interested in. I didn’t know what acting was, but I was always performing quietly to myself in my bedroom. I was never one of those gregarious children, but I loved films and loved the chance to re-create films on my own,” she said.

“My mum says she always knew — in that way that mums do. She always knew that was what I was going to end up doing.”

Macdonald is married to musician Douglas Payne. Before they met, she recalls, she was living in London pursuing her career and very lonely.

“Everything’s been a bit easier since I met Douglas. We’re from Glasgow, but we met in London. And he was at art school with one of my best friends, and so we kind of started to bump into each other, and I thought, ‘I like him a LOT.’ ”

She says marrying and having her son, now 2, shifted her outlook. “Having a baby instantly changes your whole world.

“Getting married changes your idea of your future, and you’re linking arms with somebody and going at it together.”

Though Payne is with a band, their schedules have meshed so far, she says. “He’s an amazing dad, and he’s had to do a lot more than I’m happy with. I want to be there doing it. It goes so quickly,” she said. “And everybody says that, and you get annoyed at the time. You think, ‘Yeah, that’s what people say.’ But it’s so true.”

“Boardwalk Empire” took a year out of her life. “Even when we were in New York filming the show, my son was there, my husband was there. I was working such long hours so I’d go days without seeing him, and that’s hard. The days were very long.”

She says Payne’s vocation may be different from hers, but he recognizes the need to be away from the family. “He’s close enough that he understands but different enough that I’m not living with an actor.”

‘Boardwalk Empire’

When: 9 p.m. Sunday

Where: HBO