Mary Hays was born in Southwark, London on Oct. 13, 1759. Almost nothing is known of her first 17 years. In 1779 she fell in love with John Eccles who lived on Gainsford Street, where she also lived. Their parents opposed the match but they met secretly and exchanged over 100 letters. Tragically in August 1780 Eccles died of a fever. She wrote "All my pleasures - and every opening prospect are buried with him". This may have made her outlook very solemn, and spurred her to take up writing. For the next ten years she wrote essays and poems. A short story "Hermit: an Oriental Tale" was published in 1786. It was a picturesque tale, which warned against feeling too much passion. She exchanged letters with Robert Robinson, a minister who campaigned against the slave trade. She attended the Dissenting Academy in Hackney in the late 1780s.
In 1791 she replied to Gilbert Wakefield a pamphlet with the didactic title, Cursory Remarks on An Enquiry into the Expediency and Propriety of Public or Social Worship, using the nom-de-plume Eusebia. The Cambridge mathematician William Frend wrote to her enthusiastically about it. This blossomed into a brief romance, but Frend was less enthusiastic than Hays. In 1792 Hays was given a copy of A Vindication of the Rights of Woman by Mary Wollstonecraft. It made a deep impression on her. Hays contacted the publisher of the book, Joseph Johnson, which led to her becoming friends with Wollstonecraft. Hays next wrote a book Letters and Essays (1793) and invited Mary Wollstonecraft to comment on it before publication. Although the reviews were mixed Hays decided to leave home and to try to support herself by writing. She moved to Hatton Garden. She did not have enough money to buy Enquiry concerning Political Justice by William Godwin. Boldly she wrote to the author and asked to borrow it. This turned into a friendship, in which Godwin became a guide and teacher.
Her next work, Memoirs of Emma Courtney (1796) is probably her best-known work. The novel draws on the experience of her affair with William Frend, and may also have elements of her relationship with Godwin. The heroine falls in love with a penniless man Augustus Harley, and offers to live with him as his wife, without getting married. She is rejected and then turns to Mr Francis, a character based on Godwin. They exchange philosophical letters, but in the end he advises her against becoming too emotional. The critical response to the novel was divided along political lines. Free love is seen to be aligned with social and domestic repression is shown as upholding the political order.
About this time Hays started writing for the Analytical Review, a liberal magazine. Mary Wollstonecraft was the fiction editor. It was Mary Hays who is popularly credited with introducing William Godwin to Mary Wollstonecraft. In 1797 Wollstonecraft and Godwin married. When Mary Wollstonecraft was dying, due to complications following the birth of their daughter, Mary (Mary Shelley), it was Mary Hays who helped to nurse her. She also wrote an obituary of Wollstonecraft for the Annual Necrology.
Hays and Godwin drifted apart, and she turned her attention to other writers, including Robert Southey. There is no known portrait of her in later life, but Samuel Taylor Coleridge considered her ugly. Her next novel The Victim of Prejudice (1799) is more emphatically feminist and critical of class hierarchies. It is also somewhat melodramatic. The backlash against the French revolutionary terror affected critical responses to the novel: Hays was considered too radical and hysterical. In 1803 Hays proved her determination and earnestness by publishing Female Biographies, a book in six volumes, containing the lives of 294 women. By this stage Hays perhaps realised that it was dangerous to praise Mary Wollstonecraft, and so omitted her from the list. Moving to Camberwell, Hays became known to many of the literary figures of the time, including Charles and Mary Lamb and William Blake. The last 20 years of her life were somewhat unrewarding, with little income and only moderate praise for her work. In 1824 Hays returned to London where she died in 1843. She is buried at Abney Park Cemetery, Church Street, Stoke Newington, London.