Class act Jonathan Groff is coming to West End

Jonathan Groff is looking out over Soho from a rooftop terrace bar. 'How did I get here?'he asks softly. 'All the way from Pennsylvania'As he is a star of musical theatre – a bona fide, Tony Award-nominated leading man – I feel this might be the moment for him to break into song, complete with a soft-shoe shuffle around the chimneypots. Instead, he tells me his life story over a Sprite and a salad. He grew up on a stud farm, but dreamed the impossible dream and won a starring role on Broadway aged just 21, playing Melchior in the hit teen musical

Groff's father owned two horse ranches in Lancaster, Pennsylvania. 'It was kind of a
beautiful place to grow up. Big fields, wide countryside. It's Amish country,'says Groff, still in dreamy mode, his baseball cap on backwards. Lots of people he knew – including both his neighbours – belonged to the conservative Christian sect. 'They're very sweet, beautiful people. They don't like to get their picture taken, they're not allowed to drive cars, only ride in them.'Was he always giving lifts? 'Right. My grandmother had Amish workers in her garden and I always drove them home. They're not allowed to use electricity; they're very simple, humble people.'

What the gentle Amish folk must have made of Groff, however, is another matter. He was an all-singing, all-dancing showbiz kid. 'I was passionate about theatre – obsessed. I would put on plays in the barn. I was the one reading the Stephen Sondheim biography. I directed You're a Good Man, Charlie Brown and cast myself as Charlie Brown. I would tape the Tony Awards and bring them into school on VHS, that's how much of a nerd I was.'Did the other kids think he was odd? 'I wasn't a crazy outsider – for some reason people entertained my enthusiasm and watched the Tonys with me.'In many ways he was like Jesse St James, the character he plays in Glee – driven to succeed and perhaps a little cut-throat. 'I do understand his passion, except his goes to the dark side. Mine never did. Though it could have. We've all got everything inside us, right?'

Jonathan was brought up a Methodist, but on his father's side he is Mennonite. 'Which is like a watered-down Amish. My grandfather was a Mennonite preacher. He was a strong operatic singer who would shake the whole church. I saw him in church and, although I didn't get to know him very well because, weirdly, he died on my tenth birthday, we still had a connection. He was a performer. If I got it from anyone, it was him.'

Jonathan's mother is a gym teacher. Just like Glee's fearsome Sue Sylvester? 'No, nothing like Sue Sylvester,'he laughs. 'Except she does wear a lot of tracksuits.'His father trained horses, only he wasn't allowed to ride them. 'They were for harness racing [modern-day Roman chariot racing], not riding.'Last year, when Jonathan made his first feature film, Ang Lee's low-key Taking Woodstock, about the 1969 music festival, he had to have lessons so he would be able to ride off on a white horse in the last scene. Jonathan says the truth of growing up on a ranch wasn't very romantic. 'I just spent a lot of time shovelling their remains,'he says tactfully.

A classic geek, he never rebelled. He is still close to his former teachers and his parents, who came to see him in Spring Awakening ten times. But after high school, he made a break for the bright lights. He skipped college and moved straight to New York, taking singing and dancing classes, waiting tables at a restaurant in Hell's Kitchen, and going to open auditions. 'I would turn up with my tap shoes, the whole deal.'Theatre sustained him. 'I saw Thoroughly Modern Millie six times. I was obsessed with Sutton Foster.'Foster, a brunette ingénue, was starring in the Julie Andrews role. Groff's other heroine is Juliette Binoche. 'I'm such a huge fan. At 43, she decides she wants to dance, to paint she's amazing.'

Jonathan is naturally candid but he shrinks when I mention his love life. 'There are a handful of people I'm close to but otherwise I never talk about who I'm dating.'Last year, he told Broadway.com that he was gay and proud, and he was photographed taking part in a National Equality march in Washington. Today he is more discreet. 'I never dated anyone at high school. I was focused on singing and dancing.'

In April this year, Newsweek magazine ran a piece about the pitfalls of sexuality-blind casting, citing Groff's heterosexual role in Glee as having 'something about the performance that feels off'. The Glee community jumped to defend Jonathan. 'I just felt, "OK, well, this person felt that about my performance," it's like a good or a bad review, you have to let it roll off your back. I'm an artist and an actor and I want to play people of all different types and sexualities and personalities and I hope I'll be able to do that.'

He thinks stars can be better off if they stay 'slightly under the radar'and our conversation segues into the importance of humility. 'The Amish know a lot about that. There was a terrible massacre at a school about ten minutes from where I grew up. The local milkman – not Amish himself, but integrated into their community – came into the schoolhouse and he made the male teacher and the boys leave and he tied the little girls'ankles together and massacred them. The Amish community chose not to publicise their grief; they just had a candlelit service, tore down the school and planted grass and that was it. The way they dealt with it was very moving.'

Groff's life changed when he won the role of Melchior in Spring Awakening. He was part of the original cast on Broadway for two years, with huge success. On the morning the Tony nominations were announced: 'I woke up at 8.30am – my brother was staying with me – and we waited to see if my name was on the list. That was the "aargh" moment, I wanted it so badly.'Again I feel he might have a song coming on. After all, he sang at the Tony Awards. That he didn't win didn't worry him; the nomination was what mattered. Spring Awakening also gave him a new best friend, Lea Michele, who went on to play his on-off girlfriend Rachel in Glee. The pair jokingly call each other Mom and Dad; their families have spent New Year together for the past three years. 'The Glee kids are going back on set about now, filming the second series,'he says, a little wistful that he's not with them.

Groff has a gentle charm, and his latest co-star, Simon Russell Beale, appears smitten. 'We've spent as much time together outside of rehearsal as we have in rehearsal,'Groff says. 'We've really become friends.'They've been going out to dinner together – The Wolseley is a favourite – or to see shows. Spartacus at the Royal Opera House is next on the list. 'We're opposites in many ways – I'm American, he's classically trained. I've never been to college, I don't know Shakespeare, so I said to Simon, 'I want you to teach me,'and he said, "OK, we'll start with Antony and Cleopatra." 'Where will the tutorials take place? 'We've been known to go to St James's Park and lie in the long grass and just hang out, so maybe there.'

It all started when Groff was cast in Deathtrap. 'He gave one of the best readings for a part I have ever heard,'says prolific director Matthew Warchus (responsible for the Tony Award-winning Boeing Boeing and Olivier award-winning God of Carnage). Deathtrap is a tense two-man stand-off, memorably filmed by Sidney Lumet in 1982 with Christopher Reeve in Groff's part and Michael Caine in Simon Russell Beale's. Their chemistry is essential. 'I knew Simon was a god of theatre but I'd never seen him on stage, so I left LA and took myself off to London in May
to see him in London Assurance [an early Victorian comedy in which he starred opposite Fiona Shaw]. I was completely blown away. Afterwards, we met at the stage door and he took me on a tour of the National and showed me his dressing room. He asked what I was doing the next day and I said, "Looking for a flat," and he said, "I'll come with you." He's done a really good job of making me feel welcome.'Groff is 25, Beale 49 – is there a father-son vibe? 'He'd kill you for that. We joke about it all the time. I say, "I was 12 when you were in that play." He says, "Are you trying to depress me?" '

This autodidact's need for constant self-improvement is a recurring theme. Groff left the US for the first time aged 23: 'I went on my own for a week to Rome, Florence, Sienna, Assisi. I crammed everything in. Italy really changed me. The art is so inspiring. When I went to Florence, I burst into tears in front of Michelangelo's David.'