'When I read books I certainly don't read for the plot. I read for language. I read for those sentences I try to make. A little bit of tension goes a long way'

In case you ever wondered, the Pulitzer Prize is actually a paper- weight. Carol Shields found this out when she was awarded one in April for her extraordinary novel, The Stone Diaries. You also receive a commemorative plaque, a piece of paper ("looks like a Sunday School certificate" she says) and a cheque for $3,000. "Which," Shields said, "friends at home in Canada have chortled about because it seems like a surprisingly small sum. But it translates into sales such as I have never had.''

The Stone Diaries was doing quite nicely even before it won the most prestigious literary prize in America. In Canada, where Shields lives and teaches literature part-time at the University of Manitoba in Winnipeg, it was a great success. In America, where she was born (in Oak Park, Chicago), the praise was lavish. And in Britain, where she couldn't even get published until 1990, The Stone Diaries was a Booker Prize nominee, enabling reviewers to hail a "new discovery" - a fresh term perhaps for someone who was, at the point of publication, already 57 and five novels down the line.

The Stone Diaries told the fictional life-story of Daisy Goodwill. The book was at once massive (it spanned most of the 20th century) and minute: its prose had a formidable ability to bring alive the stuff of daily routines, of cooking and working and washing. It was also a kind of skit on the biographical form. The book's endpapers included an elaborate family tree and at the centre of the book, in a thorough pastiche of historical biographies, there were eight glossy pages of photographs supposedly of the novel's characters (though, crucially, not the heroine). In fact, these were old postcards and snaps gathered from junk shops and Shields' family albums. As the book's narrator, Daisy Goodwill, remarks: "The recounting of a life is a cheat, of course."

The author of this deception, now 59, was in London last week to mark the publication here for the first time of her first and second novels. Shields is small and slight and white-haired and her voice is almost too quiet to register on conventional cassette tape. (I ended up holding the recorder towards her, like a television sports commentator conducting a post mortem after the full-time whistle.) Her hands move slowly away from her body as she speaks and she gives off an enviable degree of equanimity. Her mouth forms, almost continually, a mild smile. Shields seems amused even by the things to which she objects. On The Bridges of Madison County, for instance, the multi-million-selling romantic novel and all-purpose slush bucket: "Yes, I did read it. Awful. Incredible. It's a hoot" - these words accompanied by much laughter.

You could imagine Shields very easily as a silently observing presence in social gatherings. "Writers stand outside of events and watch," she said, echoing the narrator of Small Ceremonies, her first novel, who declares: "I am a watcher. My own life will never be enough for me. It's a congenital condition." But this is not to say Shields is prepared to blank herself out at all times. During our conversation, her feminism would occasionally surface abruptly. At the end of our interview, she asked me if I could recommend any plays in London. I thought the author of a play about bridge (Thirteen Hands, which premiered in Toronto this year) might be interested in a play about poker (Dealer's Choice by Patrick Marber). Shields immediate and only question was: "Are there any women in it?''

Shields was not an early starter : her first novel was published in 1976 in the week of her 40th birthday. (In the one moment in our conversation in which she sounded faintly melancholic, she said she wished she was 10 years younger so that she could enjoy more the travelling which is now part of her lot.) Her first book published in Britain was Mary Swann. Two more novels followed (Happenstance in 1991 and The Republic of Love in 1992) before The Stone Diaries. Now, after Various Miracles, a collection of short stories published last year, her publishers have gone back to pick up the first two novels (Small Cermonies and The Box Garden) and Shields finds herself talking about books she wrote nearly 20 years ago.

"I had to re-read them," she said, "because you forget a lot of things. People's names and whole scenes. These books are not very dense. They're economically written and I think I'm less economic now. I didn't have much time to write when I wrote those books. Actually, I didn't have much time to read, let alone write."

Around then, she would have been mostly occupied by her family. Shields has four daughters and one son. (She shows everything she writes to her daughters, who make suggestions. One of them wrote "yuk" in the margin at one point in The Stone Diaries and Shields promptly took out the offending line.)

She met her husband, Donald, in the late 1950s in Scotland on a trip there organised by the British Council. She was studying literature on an exchange programme at Exeter University; he was a post-graduate engineering student from Canada, studying at Imperial College London. She had her first child just nine months into the marriage at 22.

"It was just how we lived. We all seemed to marry right after our degrees and at the end of the first year we all had babies. It seems incredible now. I don't know where I had the energy, but I clearly had a lot of it in my twenties."

You would have got good odds on Shields becoming a full-time academic. Yet after her MA thesis, for which she researched the minor Victorian novelist Susanna Moodie, she dropped out, largely for her family but also to try to become a writer. Her first literary success was when the Canadian Broadcasting Corporation awarded her a poetry prize in 1965. She was 29. "I wrote seven poems to enter, very much borrowed from the Philip Larkin style. I borrowed his sense of depression, too, so all my friends were phoning to see if I was having a nervous breakdown." At the centre of the collection was a poem inspired by her small son. He was having lunch when a plane passed overhead, causing him to look up and say: "The pilot doesn't know I'm eating an egg." "And of course, I thought that was a very existential thing to say," Shields said, laughing. "And I wrote quite a neat little poem around it.''

Two collections of poetry followed, Others and Intersect. Meanwhile, the Sixties came and went. "I remember watching a love-in in Toronto in a big public square and thinking how wonderful it was and how I'd like to be a part of it. But I was married, I had children, I was living a very conventional life. I did have some very short mini-skirts ... And I went to hear Allen Ginsberg read Howl - that was thoroughly Sixties. And my husband had long hair and wore only jeans for 10 years. But we were very conventional."

When it came, Small Ceremonies was, perhaps unsurprisingly, a novel about a woman researching into the minor Victorian novelist Susanna Moodie. ("I had all this material left over that was inadmissible because it was speculative.") Shields was encouraged when she received, "completely out of the blue", a letter of congratulations from the novelist Alice Munro, whom she had always admired.

She had found it hard for a time to convince herself that becoming a writer was a worthwhile ambition. "People that I knew were going off and being politically active and I thought maybe I should be doing that rather than sitting making up stories. So I did feel uneasy, but not cripplingly so. I remember when my first book was published, an Ottawa bookstore had a window filled with it. And I couldn't walk by that bookstore. It felt so public, I felt embarrassed, exposed. I've got over that, but it was curious. Somehow I had sat there writing this thing without ever thinking it was going to end up as a book."

Late in the 1980s, Shields was inspired by a quotation she came across from the author Patrick White, who said he never bothered too much about plot but simply concentrated on "life going on toward death". It emboldened her to worry less about story and concentrate on language. "I wish I'd known that quote all along," Shields said. "When I read books, I certainly don't read for plot. I read for language. I read for those sentences that I try to make. A little bit of tension goes a long way with me."

She said that, throughout all those early years of writing, she had no particular ambition to sell her books in America and Britain. "I had a following in Canada - a small one. But I was happy with that. Sometimes I would tell myself I should think more about where my books were selling, worry more about my 'career', but mostly it didn't bother me."

She recently finished a script for a film version of The Republic of Love, which was something of a struggle. "I don't go to movies much. I'm not very film-literate." Still, the New York Times has suggested that the film could do for Winnipeg what Sleepless in Seattle did for Seattle. Shields rather fears that, if Hollywood gets hold of the script, the film will be set in Seattle anyway.

She heard about her Pulitzer at a lunch given after a reading in Minneapolis. "The publisher phoned and said, 'Are you sitting down? I've got some news for you.' And I was sitting down and I was glad I was sitting down." After champagne, Shields returned to her hotel. "And then it got a bit frightening, a little spooky." She was under siege for a while from the press. She stood in her room and watched messages being pushed under the door. When her husband tried to get through on the phone, the hotel switchboard informed him he was number 61 in line.

She recalls finding herself, later that day, face to face with an old- school news-reporter from New York, brandishing a notebook and pen. Shields began talking to him, as she put it, "in her literary persona", but he cut across her somewhat impatiently, barking: "Gimme a lead, gimme a lead."

She still hasn't worked out what she could have said to satisfy him. "I don't think writers have any corner on insight or wisdom at all. What they have is a facility with language. I like sentences. I like to work on sentences and make them feel right. I will tinker with them all day. I don't have patience for other things, but I seem to have endless patience for this."