He started in classical music, but Conor Linehan has branched into jazz,dance and, now, the world of ghosts, writes Arminta Wallace.

Last week he recorded the incidental music he composed for the third act of Chekhov's The Cherry Orchard, at the Abbey Theatre, which involves a Jewish string band. Then it was off to Liverpool to do the soundtrack for a classic Spanish play, complete with castanets, guitars and all the rest of it. Tonight he's heading back to London to rehearse a show of Brecht and Weill in which he collaborates with the jazz singer Eva Meier. And come May he'll be on his way to China with Mermaids, whose music he wrote for CoisCéim Dance Theatre last year. The world, it seems, is Conor Linehan's oyster.

But hang on a second. Klezmer? Castanets? Cabaret, for goodness' sake? Didn't he start off as a straight-down-the-middle classical pianist? He swirls his cappuccino and looks hurt. "I'm still a straight-down-the-middle classical pianist," he protests. Then he adds, with a grin, "in my own little way".

It began in the usual way: lessons at the Royal Irish Academy of Music - "I studied with Thérèse Fahy, a fantastic teacher" - followed by a degree in music and English at Trinity College in Dublin and a couple of years of private postgraduate study in London. "And then," says Linehan, "I started trying to make my way as a professional pianist. When I came back to Dublin in 1997 I was doing the rounds to see what work I could rustle up, and I went in to the Abbey and said to Patrick Mason, look, if anything comes up, anything at all, give me a call."

The Abbey might seem a curious calling place for a classical pianist. But given Linehan's family background, it would have been altogether more curious if he had not drifted theatrewards: his mother is the actress Rosaleen, his father the playwright Fergus. His brother, another Fergus, is director of Dublin Theatre Festival.

In due course he was asked to coach the actor Sean Rocks to play the piano for the Peacock's production of The Wake. "One thing led to another and then to The Colleen Bawn, which was a really, really enjoyable show." It was also extraordinarily successful. "It went to the Royal National Theatre in London, and then I got offered another show in London and then another; and then I did a couple of shows at the RSC." He pauses. "It's funny, you know? Your career kind of chooses you rather than you choosing it."

But he still does play classical piano; in fact Linehan is about to make his début with the RTÉ National Symphony Orchestra, as soloist in Ronan Guilfoyle's Piano Concerto. "I played it with the RTÉ Concert Orchestra a year and a half ago. It was originally commissioned for a conservatoire-trained Russian jazz pianist who had worked with Ronan before, an absolutely astonishing pianist. For various reasons he had to pull out, so I got a call from Ronan saying, Do you fancy this? I said, You bet. I spent the entire summer just holed up, learning it." This is a concerto that, as the guy says, contains a lot of notes. Linehan wriggles his fingers. "And a lot of it sounds improvised but actually isn't. The trick is to give it that spontaneous feel. Actually, when Ronan was writing it originally I think he did leave certain bits to be improvised. But when it came to me . . . well. I mean, I used to play in bars and restaurants, but I'm more of a Gershwin, Cole Porter kind of guy. Actually, I've been getting more and more frustrated in recent years with my very obvious limitations as a jazz pianist. Anyhow, he wrote out every single note - and I figured it out, note by note by note."

This meant taking the classical approach to the fiendishly complex rhythms of jazz. "When you look at the page you think, What the hell's going on here? And you're trying to figure it out, and you're trying to count it. And then, when you get it, you're, like, Yeah." He clicks his fingers lazily - the most natural rhythm in the world.

He has another opening night this week, with today's return of the highly successful The Ghost Show, from last year's Dublin Fringe Festival, where it was called Things That Go Bump, for a short run at the Helix. Linehan grins. "I have huge faith in this show. I just love doing it. It has no storyline as such, it's just a series of songs, either atmospheric and dark or quite comic, unified by ghostly subjects. There are two singers, Susannah de Wrixon and Mark O'Regan, and it's directed by Caroline Fitzgerald and the music is by me and the words are by my dad."

Linehan insists that classical music is at the centre of his musical life - "I call it the mother ship, because all the other interests have generated outwards from there" - but his musical interests clearly range across a much broader range of styles than that of the average classical pianist. He speaks as passionately about Schubert as he does about Kurt Weill. At the moment he's listening to John Cage, Nick Drake, Brahms, a little Arvo Pärt and a lot of Neil Hannon's Divine Comedy. As far as role models for his own multibranched career are concerned he shrugs unconcernedly. There's a composer in London called Jonathan Dove who writes for music theatre as well as concert performance; there's the pianist Joanna MacGregor, who crosses boundaries all the time. As to whether he'll be able to keep all the balls in the air indefinitely he doesn't really know.

One thing's for sure, though: he's going to keep on composing. "After graduating I didn't know what to write. I was very confused. I knew I had some sort of a gift, some sort of facility with this, but I was asking myself not just what do I write but why do I write. Style in music has become so fragmented that you almost choose a style in which to write. In Trinity there's very much a Second Viennese School orthodoxy, which I found more limiting than liberating. I mean, I love \ Pierrot Lunaire and the Berg Violin Concerto and some of Webern's music, but it just didn't seem right for me to write that sort of stuff. I think that's why I was so drawn to theatre music. It's very specific. You're asked to write to a particular brief, which could be anything from Jewish string music to Spanish songs to atonal music to bebop jazz."

Which is, more or less, where we came in. "I just hope," Linehan adds, "that as I keep doing it some sort of voice of my own will emerge."

Conor Linehan plays Ronan Guilfoyle's Piano Concerto with the RTÉ National Symphony Orchestra at the National Concert Hall on March 9th at 1.05 p.m., as part of the Horizons series of concerts. The Ghost Show opens at the Helix, Dublin, tonight