Few records of Mary Astell's life have survived. As biographer Ruth Perry explains, "as a woman she had little or no business in the world of commerce, politics, or law. She was born, she died; she owned a small house for some years; she kept a bank account; she helped to open a charity school in Chelsea: these facts the public listings can supply." Only four of her letters were saved and these because they had been written to important men of the period. Researching the biography, Perry uncovered more letters and manuscript fragments, but she notes that if Astell had not written to wealthy aristocrats who could afford to pass down entire estates, very little of her life would have survived.
Mary Astell was born in Newcastle upon Tyne on 12 November 1666, to Peter and Mary (Errington) Astell. Her parents had two other children, William, who died in infancy, and Peter, her younger brother. She was baptized in St. John's Church in Newcastle. Her family was upper-middle-class and lived in Newcastle throughout her early childhood. Her father was a conservative royalist Anglican who managed a local coal company. As a woman, Mary received no formal education, although she did receive an informal education from her uncle when she was eight, an ex-clergyman named Ralph Astell whose bouts with alcoholism prompted his suspension from the Church of England. Though suspended from the Church, he was affiliated with the Cambridge based philosophical school which based its teachings around radical philosophers such as Aristotle, Plato, and Pythagoras. Her father died when she was twelve years old, leaving her without a dowry. With the remainder of the family finances invested in her brother's higher education, Mary and her mother relocated to live with Mary's aunt.
After the death of her mother and aunt in 1688, Astell moved to Chelsea, London, where she was fortunate enough to become acquainted with a circle of literary and influential women (including Lady Mary Chudleigh, Elizabeth Thomas, Judith Drake, Elizabeth Elstob, and Lady Mary Wortley Montagu), who assisted in the development and publication of her work. She was also in contact with the Archbishop of Canterbury, William Sancroft, who was known for his charitable works; Sancroft assisted Astell financially and, furthermore introduced her to her future publisher.
She was one of the first English women to advocate the idea that women were just as rational as men, and just as deserving of education. First published in 1694, her Serious Proposal to the Ladies for the Advancement of their True and Greatest Interest presents a plan for an all-female college where women could pursue a life of the mind.
In 1700, Mary Astell published Some Reflections upon Marriage. Astell wittily critiques the philosophical underpinnings of the institution of marriage in 1700's England, warning women of the dangers of a hasty or ill-considered choice. The Duchess of Mazarine is used as an example of "the dangers of an ill Education and unequal Marriage". Astell argues that education will help women to make better matrimonial choices and meet the challenges of the married state: "She has need of a strong Reason, of a truly Christian and well-temper'd Spirit, of all the Assistance the best Education can give her, and ought to have some good assurance of her own Firmness and Vertue, who ventures on such a Trial".
Astell warns that disparity in intelligence, character, and fortune may lead to misery, and recommends that marriage be based on lasting friendship rather than short-lived attraction. A woman should look for "a good Understanding, a Vertuous Mind, and in all other respects let there be as much equality as may be." Astell expanded on this theme in response to critics in the third edition of Some Reflections upon Marriage.
After withdrawing from public life in 1709, Astell founded a charity school for girls in Chelsea as a token of the Society for the Propagation of Christian Knowledge, organizing the school's curriculum herself with likely financial support from her patrons Lady Catherine Jones and Lady Elizabeth Hastings. When she was sixty years old, she was invited to live with Lady Catherine Jones, where she resided until her death.
Astell died in 1731, a few months after a mastectomy to remove a cancerous right breast. In her last days, she refused to see any of her acquaintances and stayed in a room with her coffin, thinking only of God; she was buried in the churchyard of Chelsea Church in London. Astell is remembered for her ability to debate freely with both contemporary men and women, and particularly for her groundbreaking methods of negotiating the position of women in society by engaging in philosophical debate (Descartes was a particular influence) rather than basing her arguments in historical evidence as had previously been attempted. Descartes' theory of dualism, a separate mind and body, allowed Astell to promote the idea that women as well as men had the ability to reason, and subsequently they should not be treated so poorly: "If all Men are born Free, why are all Women born Slaves?"