The McGarrigle sisters have had a chequered musical career, but they are happy whether in or out of the limelight, they explain to Joe Breen

It is often said you should avoid meeting your heroes as they will invariably disappoint. So the arrangement to meet Canadian duo The McGarrigle Sisters was one I approached with mixed feelings. Twenty-nine years after it was released, their debut album, Kate and Anna McGarrigle, remains a personal desert island disc. Their career has just about had more starts than stops. The way they tell it - and they tell it with self-deprecating humour, bare-knuckle honesty and can-you-believe-it surprise - everything just happened, or didn't as the case may be.

"We kind of fell into the music business," says Kate, at 59 the junior by 18 months. Anna nods and wonders if she should clarify this statement. They do this a lot, never directly contradicting each other but always willing to shed a little more light. They are unpretentious and engaging. You sense that they enjoy what they do, but there is much more to their real world than the thought of playing a string of gigs.

There are three distinct phases to their career. In the first, essentially the second half of the 1970s, they stumble upon a recording career to the bemusement of themselves, their producers and their record label. Joe Boyd, the folk-rock producer best known for his work with Fairport Convention, Sandy Denny et al, and Greg Prestopino, an American renowned for his ability to structure a good ballad, are called in to produce the album. Their relationship is a disaster but the album is a triumph of close harmony and naked emotion. The sisters insist the two men didn't see eye to eye, with one seeking deep ballads, such as Anna's tearjerker, Heart Like A Wheel ("the first song I ever wrote") and Kate's Talk to Me Of Mendocino, and the other forcing the folk-rock pace of The Swimming Song.

In this period Kate marries and separates from Loudon Wainwright III, after the couple have two children, Rufus and Martha, themselves destined to become stars. The relationship provides lots of material for Kate's agonised ballads and Wainwright's bitter-sweet commentary.

Then came the awkward follow-up Dancer With Bruised Knees (1977) and the clunky third collection Pronto Monto (1978). So after an auspicious start they sink into obscurity. The critics still love them but Warners Bros pulls the plug by mutual consent and leaves them with debts of about $25,000.

They return to their home town of Montreal where a local French Separatist helps underwrite the recording of French Record, a dignified and haunting mixture of original and traditional material sung in French. This is their second period. There follows a reasonable collection called Love Over and Over (1982) before a long silence ends with the release of another solid collection, Heartbeats Accelerating in 1990.

Their third period is marked by the release of the adventurous and captivating Matapedia in 1996 preceded by The McGarrigle Hour, a homely collection of traditional songs and ballads with the whole family, Loudon included, plus friends Emmylou Harris and Linda Ronstadt. This was Joe Boyd's idea. "Joe has been instrumental in us having any kind of a career," says Kate.

But as engaging as The McGarrigle Hour was, Matapedia is the more important recording. For the sisters it represented something new, something they had been working on for years. Matapedia had attitude and ambience similar to Emmylou Harris's breakthrough Wrecking Ball. Then silence again until this year's La Vache Qui Pleure and an upcoming Christmas album on Nonesuch. All this fitful activity begs the question: are you serious about this music lark or is it just something you do (and are very good at)?

Kate: "It's both. This is what we've been doing out whole life."

Anna: "But it's not a real commitment."

Kate: "That's true. People have always said if you want to build a career you have to work at it. I remember one year we did just 13 gigs. Yes I think you've got to make a commitment, though that doesn't mean it is going to happen for you . . . I think when record companies look at us they say to themselves: 'they'll sell X number of records, which is not a lot'. They know they'll get their money back, but not much more."

Anna also has a theory as to why they never hit it big, apart from the fact that they recorded and played little and were otherwise occupied each raising two children. "We never did buy that big house in Los Angeles. There was talk - 'oh you guys have got to come to LA' - and if we had gone things might have been a lot different. I mean [blues singer] Maria Muldaur was living in LA, drinking Champagne on her porch and walking around naked. [Both women to burst out in laughter.] So that's what life in LA was like. But it just didn't happen that way for us."

Kate never remarried - "once was enough". Neither is she particularly bothered that ex-husband, son and daughter all tend to write about their personal lives, her role included. And she has a theory as to why Loudon Wainwright's songs tend to include all manner of personal detail. "His father was a journalist and so is he. He just writes about what goes on around him."

But you sense they are very happy in their own skins. "I think what we are doing now, and have been doing for the past 10 years, is engaging with one another more onstage," says Kate. What they are trying to achieve, adds Anna, is greater "emotional intensity" when they perform.

And Kate is now a celebrity, even if only because she is the mother of rock stars. "Oh I'm the mother of Rufus and Martha and I really love that. I'm gaining new respect. And Rufus takes me to grand places. This year he did the Venice Biennale with Gilbert and George and all that crowd. So I find myself at five in the morning drunk as a skunk trying to get across the canal with a Hapsburg no less. On the other hand Martha and I will go off on a shopping spree . . . I really like hanging with them, it's fun. And you know there is a short amount of time you can do that before you are on a cane or a walker."

But that is some way off. For now these two Canadian sisters with a convoluted bloodline - "my father had Irish blood; Rufus was in Donegal and he rang to say that there were loads of McGarrigles in the phonebook" - are just happy doing what they do best: make beautiful music of heart and soul. "We never had intended to do this you know," says Kate. "There was no plan. So we landed ok. It's kind of like an airplane. We had a great take-off but then we hit some turbulence. But we're still up there." And then both look at each other and laugh.

Kate and Anna McGarrigle play Dublin's Vicar St on Wednesday