Actor Robert Sean Leonard is a wise man. Over the past 30 years he has carved out a career with the perfect balance of enjoyment, starring on stage in Camelot and Pygmalion and in the award-winning TV series House as Dr James Wilson, while retaining just enough fame from films such as Dead Poets Society to keep him in directors’ minds but off the paparazzi radar.

But on top of all of that, and luckily for us, he is a man wise enough to listen to his wife’s advice. Because despite such a long and distinguished career, he first had serious misgivings about taking playing the part of Atticus Finch in the stage version of Harper Lee's  To Kill a Mockingbird.

“I couldn’t see myself in the role. It is very tricky because the film version with Gregory Peck is so loved and his interpretation is so iconic, so it made me a little nervous to take it on,” says the 46-year-old about being approached to play the part at the Regent’s Park Open Air Theatre in 2013.

“I thought ‘that’s insane, I’m not a 50-something, southern, soft-spoken, morally-upright lawyer.

“But my wife wanted to go to London and she said, she’s much smarter than I am, ‘any job you’ve been nervous about in the past has turned out to be a great thing’, and the more I read it and thought about it, the more I felt inclined to take on the challenge. I’m certainly proud of where I’ve got to.”

The critically acclaimed production went on to tour the UK with Daniel Betts taking on the role of Atticus, while Robert went back to the States to raise his two daughters.

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Robert Sean Leonard (Atticus Finch) and Ava Potter (Scout Finch). PHOTO: Manuel Harlan

But now returning to star in its run at the Barbican, he has found fatherhood has given him a deeper understanding of the story, which he first read aged 13.

“I can relate to Atticus in 99 ways,” says Robert who was born in New Jersey to a nurse and Spanish teacher and had his first acting job aged 14.

“There’s a scene in the story (which I’m going to assume you know. If not, why not?) when Atticus is explaining to his daughter Scout why he is defending a black man accused of raping a white woman, when so many people are against it, and he tells her ‘Hold your head high and keep your fists down’.

“There are moments like that when I can understand him and I live 100 per cent in that moment as myself and I don’t think about Gregory Peck or the audience or anything other than this girl in front of me.”

He has been busy rehearsing with almost an entirely new cast for this production and relearning all the lines and although he says it is a delight and doesn’t feel like work to him, he is now looking forward to his family joining him in London this week.

His eldest daughter has already pumped him for information about his young co-stars and Robert says: “I think for a six-year-old it must be such an overwhelming image to see your father in front of 1,200 people under lights. I don’t think it’s about her wanting to perform, I think it’s like a girl looking at an orca at an aquarium.”

There is a long pause before he adds: “I just realised I compared myself to an orca.”

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Despite acting from a young age and co-starring with Robin Williams and Ethan Hawke in Dead Poets Society, Robert has managed to avoid the goldfish bowl of fame.

“There are ways that actors enter the public consciousness through film, that launch someone instantaneously to stardom, like Kevin Bacon in Footloose,” he explains.

“But luckily that wasn’t what Dead Poets did for us. It was very, very popular and successful but no one really knew our names and I think for me it was a nicer way to start.

“I wasn’t on the red carpet photo scene and my career has stayed in that vein. I’ve never felt a part of that crowd. I look at Ben Affleck and think ‘he’s a movie star’ and I’m an actor, I just do jobs.”

The cast have kept in touch, commiserating over Robin William’s death last year, and Robert says watching Ethan Hawke in Boyhood was “like I was watching my younger brother winning a football game’.

Robert himself became a household name during his eight-year stint on House and has appeared in The Good Wife and Law & Order SVU and while theatre has remained his first love he hasn’t ruled out doing more television.

“One of the reasons I did it in the first place was because after 30 years of theatre I had no money.

“It’s not really a money-making scheme, a job like this. I do it because I love doing it.

“I love the act of performing something from A to Z in one sitting as opposed to chopping it up day by day on set, having my days free and going to the theatre at night, the live audience and the connection I have with these people in real time and the writing, it’s hard to beat the great playwrights.”

To Kill a Mockingbird by Harper Lee has been back in the headlines this year after she announced she would be publishing her second ever novel Go Set A Watchman, 55 years after her first, which Robert describes as a perfect book.

“It’s a much more interesting story than I first thought. It seemed too simple, there’s this horrible accusation and this morally upright man who goes the distance and fights for him. But its more complicated then that.

“There are basic pillars that Atticus has built his life around – like that the law is glorious and supreme and that violence is always wrong – and that’s not quite the message of the book.”

The climax of the story sees the town sheriff debate with Atticus over whether to follow the law or do what he thinks is morally right, finally deciding on the latter. And Robert believes his character turns out not to be such a perfect man after all.

"Without a doubt I think the sheriff is right – just because something is legal doesn’t mean it’s right.”

Like I said, Robert is a wise man.

Barbican, Silk Street, EC2Y 8DS, until July 25. Details: 020 7638 8891, barbican.org.uk, tokillamockingbirdplay.com