In time, Martha became as precious to Freud as life itself. And yet the woman who shared his life for more than half a century has been neglected by Freud scholars. Just over 50 years after her death, Martha has emerged to claim her due in a biography by Katja Behling-Fischer, a writer from her home town of Hamburg. Behling-Fischer has sifted through family archives and some of the letters she wrote to Freud - most are expected to remain locked away for another five years at least, as they are being edited for publication at a snail-like pace.

The biography depicts Martha as a spirited woman who, like her husband, was ahead of her time. She inspired Freud both intimately and professionally, and their relationship reveals a Freud far removed from the stereotype of the dispassionate trailblazer of psychoanalysis. The book has been welcomed by Anton Freud, one of Martha's grandsons, who says she was much more than 'just the wife, or someone who cared for the house and children'.

Martha, born in 1861, was the second child of a well-established Orthodox Jewish family. Her grandfather was the leading rabbi of Hamburg and her mother, Emmeline, was very religious and, as tradition decreed, had cut her hair when she married. This illustrious background was no guarantee of wealth: when Martha was eight, her father, who sold advertising space in local newspapers and traded in bonds, was arrested and jailed because he failed to pay his creditors. He was freed after 10 months, but only because his family could not survive without him. His employer agreed to hire him again, but on condition he move to Vienna to work in a subsidiary, which he did.

The family's fortunes improved, but when Martha was 18 her father died. For her mother, the priority was to ensure that Martha found a husband who would fit her religious background and give her a comfortable position in society.

Martha was almost 21 when she was invited to the Freud apartment in April 1882. Sigmund, a medical graduate, usually dined alone in his room so he could continue his studies of neurology.

But on the evening when the doe-eyed Martha appeared, her hair as usual parted down the middle and tied back clear of her long, pale face and sensual mouth, she made such an impression that he stayed and had dinner with her, his parents and five siblings. For Martha too, it was love at first sight. And according to a friend, one of the reasons she found him attractive was that he reminded her of her father.

Martha was used to suitors - she was well educated, came from a good family and was attractive, a slim girl in the figure-hugging dresses of the time. She had come close to an engagement with an older man, a salesman, but her brother put an end to it, saying that she didn't really love him. Eventually she admitted that he had been right.

Freud was no womaniser. Only one girl, Gisela, had made an impression on him as a teenager and, as he admitted half-jokingly, he could have done with more experience of women in his youth. His wooing of Martha was fast but sporadic. They met several times in the weeks that followed, for walks in the Prater amusement park on the city's outskirts. At first they were never alone: Minna, Martha's younger sister, was the escort that propriety imposed on them. Freud sent Martha a bouquet of roses, with a couple of poems he had chosen. In his notes to her, he compared her to a princess, and her lips to roses and pearls. And yet he was shy and insecure: when, in late May, during their first walk alone, Martha refused his gift of a bunch of oak leaves, he was sure she didn't want him and agonised over his perceived rejection. Slowly, Martha placated him.

Martha's patience was again tested a week or so later. Freud happened to see her making a money pouch for her cousin, and concluded he had been jilted. Martha forgave him his possessiveness and they exchanged gifts: she baked him a cake, and he gave her a copy of David Copperfield. On June 13, she was invited to dinner at the Freud home, and this time he took her place card as a souvenir. Martha pressed his hand under the table. That week, she received her first letter from Freud, in which he addressed her by the polite Sie (you) - the more intimate du came later. 'Precious Martha, how did you change my life?' he began.

When her mind was made up, Martha was direct. 'Sigi, my Sigi,' she wrote in an early letter. 'Today for the first time I call you by your name... My darling, I am happy, yes, happy as I have never been in my long life.' She gave him a ring that had belonged to her father, and he, too poor to afford anything else, made a copy of it and gave that to her. By mid-June, they considered themselves engaged. Freud saw this as a triumph - she had chosen him despite his poverty and his atheism.

They kept their engagement secret. Martha's mother had told her daughter all she objected to about her suitor. Emmeline had high expectations for her daughters. She couldn't accept the son of a Jewish wool merchant with no money, no proper job or footing in society, who was also an atheist.

Martha would have none of it, and went on seeing Freud as often as she could. When she saw how determined her daughter was, Emmeline took the drastic step of abandoning Vienna and taking her daughters to the town of Wandsbek, outside Hamburg. Emmeline had never settled in Vienna anyway, but Martha was in no doubt that her relationship with Freud was the reason for the decision to move in the summer of 1883.