Muriel Spark's biographer Martin Stannard tells why her native city was pivotal to her artistic exile

IN APRIL 1962, Muriel Spark briefly returned to Edinburgh. She was 44 and on the brink of becoming a major literary star. All the glamorous parties and artistic potential of New York lay before her. She had written seven novels, among them The Prime Of Miss Jean Brodie, completed in just four weeks. Now her father was dying in the Royal Infirmary.

While her mother, brother and son were together in Bruntsfield, in the same house in which Spark grew up, she was alone in the North British Hotel. Propped up at the window so she could look out at the castle, Arthur's Seat, and Princes Street Gardens, she felt "an inpouring of love" for her native city. "It was Edinburgh that bred within me the condition of exiledom," she wrote.

It's a telling snapshot of Spark midway through her life: alone, detached, unsentimental even in grief, belonging to Edinburgh but also an outsider, a hotel guest in her own city. In the first biography of Spark, arriving three years after her death, author Martin Stannard describes this moment as "the hinge of her life, the point at which the second half of her existence began to rewrite the first".

"Muriel was so unsentimental that she didn't wish to be seen to have suffered," says Stannard, who first met Spark in 1992. "I thought I couldn't write a truthful biography without explaining just how much she had suffered in her early days." Spark's experiences in Africa (where she hid her husband's gun in fear that he would shoot her), her years of penury in London struggling as a poet, her complex relationships with men, her volatile moods and her legendary spats with her publishers – all were key to understanding her as a great writer of uncompromising vision, wit and economy.

Stannard's biography may not be stuffed with the controversies that some expected, after ten years of work as well as a formidable subject who was apparently none too pleased with the finished manuscript before she died. However, it does paint an intriguing and sympathetic portrait of a woman who was much more passionate than she led people to believe.

"She wanted to appear unemotional," says Stannard. "It was about her public image, the implacable exterior that she would present to the world. The stuff I wanted to include was about her losing her temper, or sacking somebody, or an outburst that brought her to life. You suddenly saw the mask crack a little. Spark may have told journalists that writing was 'the easiest thing I had ever done', but the truth was she suffered depressions when she finished a book.

"She was an extraordinarily strong woman. Intellectually she was fascinating, and psychologically she was like no-one I had ever met. She wanted to present an image of herself that was inaccurate. She didn't want me to quote any bad reviews, for example. But when you do a masterpiece like Brodie and there are bad reviews in the British press it's fascinating that people were so blind." Despite an entire issue of The New Yorker being devoted to Brodie – an accolade never before granted to a woman – British reviewers were baffled.

When Stannard first visited Spark in Tuscany, she led him to a table obscured by stacks of files, the archive that was about to be moved to Edinburgh's National Library. "It's the story of a writer's struggle," she told him. "Treat me as though I were dead." Did she mean it? Stannard laughs. "I researched with total freedom and encouragement from her," he says. "I did whatever I wanted and wrote whatever I wanted. Then, when she saw the book, she wasn't entirely delighted. It had been read by a lot of senior people before it went to Muriel and nobody had said this is some kind of attack on her. She thought it was, and that was beyond me."

A rigorous intellectual from a working-class background and a stoical woman brought up in "the city of Calvinism, high teas, and loveless alliances", as she put it, Spark saw herself as an artist years before anyone else did. She was determined to be free. Her life as a writer depended on it. The Spark of Stannard's biography had no truck with self-pity, found emotional displays embarrassing, struggled with intimacy, and in later years was plagued by a sense that she was going to be betrayed.

"Muriel had a kind of anxiety throughout her life about people betraying her," says Stannard. "There is a lot of that in Brodie. Most people I interviewed had been very fond of her. Quite a few of them were astonished by how they seemed to have cultivated her disfavour. In many ways she was a postmodern woman not just in her writing but in the way she lived. She lived as a free woman and for people, particularly men, that was unnerving."

It is partly through this prism that Stannard views her relationship with her son Robin, who grew up in Edinburgh with Spark's parents as she sent money back from London. Robin was born in Africa, where Spark was forced to leave him in order to escape her husband. She was adamant that she never abandoned him. "The problem people had was how she could have allowed her parents to bring him up. To Muriel, that was a sentimental way of looking at it. She didn't have any money so she couldn't bring him up in London, which is where she had to be if she was going to be a writer."

Years later mother and son would fall out publicly over the family's Jewish ancestry (Robin had long before converted to Judaism and Spark to Catholicism) and in the end he was excluded from her will. But there had been a vast distance between them throughout his life, and Robin refused to speak to Stannard for the book. "I sent a copy and didn't get a reply," he says. "I would have been very interested to hear his side of the story and I thought it would have been in his interest to tell it."

When Spark went to New York, and later to Rome, she powered her way through artistic circles, "mercurial, forceful, a pyrotechnic conversationalist". She was the life and soul of cocktail parties attended by WH Auden, Stephen Spender, James Baldwin and John Updike. In Rome the Italians viewed her as Kafka in a skirt, though she said she was more like Lucrezia Borgia in trousers. Yet she felt she couldn't trust anyone. "Almost everyone she knew closely," writes Stannard, "at some stage received the brush-off direct, a furious corrective letter, or plain silence."

Following sexual relationships with the writers Howard Sergeant and Derek Stanford – who did go on to betray her by selling her letters – she more or less remained alone. "One can never know this, but I think she was as anxious about physical intimacy as she was about personal intimacy," says Stannard. "The most important thing in her life was her writing. Her most important relationship, in a sense, was with her readers."

Yet there was also Penelope Jardine, an artist whom Spark first met in Rome at a hairdresser's in 1968. Eleven years later, she went to live with her in Tuscany and remained there until her death. They lived and travelled together as companions, Jardine taking care of Spark while she continued to write. When Spark died, it was Jardine who was entrusted with her estate. "She found somebody who would look after her and that's exactly what Penelope did brilliantly," says Stannard, who states early on in the book that Spark was not a lesbian. "She did the driving, the entertaining, and it was her house, not Muriel's. A friend of theirs remarked that she was like the traditional writer's wife."

In Stockbridge I meet Muriel Romanes, who is directing one of Spark's greatest and most savage novels, The Girls Of Slender Means, for the stage. It's the first time that Spark has been adapted for the stage since Brodie in the Sixties. "I think people worry about adapting her," says Romanes. "I always thought Spark should have been done more. Her books make you look at other ways of producing theatre because they're fragmented, non-linear, like shards of glass."

Laurie Sansom, who is rehearsing a production of Brodie in London that is also coming to the Fringe, is equally devoted to getting more of Spark's work on stage. "It's a very unique vision, very questioning, totally uncompromising," he says. Next he plans to adapt The Driver's Seat, Spark's favourite of her novels.

"She should be accepted as a major writer in the European canon," says Stannard. "She ought to be regarded in the same light as Virginia Woolf, or any of the great modernist writers."

He refuses to feel sorry for her. "There was a certain amount of tragedy in her life but the great thing about Muriel was that every time she came up against a problem she overcame it," he says. "She may have felt wounded by Stanford's sale of her letters, but when she got the offer of buying them back she went to look at them, laughed, and said it's a wonderful collection, I'm sure you'll have no trouble selling it. Then she walked out, 'head up, up' as Miss Brodie always instructed her girls." v

The Girls Of Slender Means, Assembly Rooms, Edinburgh, 6-30 August. The Prime Of Miss Jean Brodie, Assembly Hall, Edinburgh, 6-30 August. Muriel Spark – The Biography by Martin Stannard is available now, and the author appears at Edinburgh International Book Festival 18 August.