This ingeniously constructed double biography tells the story of a mother and a ­daughter, two writers, who did not know each other. Mary Wollstonecraft, the author of A Vindication of the Rights of Woman, died of septicaemia ten days after giving birth to Mary Godwin, later best known as Mary Shelley, the author of Frankenstein. Very different in character and interests – Wollstonecraft was more political, Shelley more scholarly – both women demanded a rare romantic and intellectual freedom that cost them dearly but pushed the boundaries of possibility for later generations.

Wollstonecraft was probably the greater pioneer of the two. Born the second of seven children to a drunken bully of a father and a passive mother, she felt keenly the absence of formal education for herself and her sisters, an injustice that inspired works such as Thoughts on the Education of Daughters and Vindication. A resourceful woman, she not only earned her own living from a young age but cared for her younger sisters for long periods of time.

Godwin had potentially more stable beginnings, as a daughter of Wollstonecraft’s grieving husband, the philosopher William Godwin, the author of Enquiry ­Concerning Political Justice. Thanks to her father, the young Mary received a better education than did many of her male peers. Yet her dead and already notorious mother haunted her. Throughout her life, she read and reread Wollstonecraft’s work and she and the poet Percy Bysshe Shelley often met and talked at her mother’s grave in St Pancras. They may even, Gordon speculates, have first made love there. Gordon later suggests that Frankenstein is best interpreted as a story of the horrors that follow when a mother’s love is absent.

The profound perils of sex, romance and motherhood resonate throughout these pages. Wollstonecraft travelled alone to revolutionary Paris, at first enthralled and later horrified and threatened by Robespierre’s reign of terror. Here, she fell in love with a charismatic American adventurer, Gilbert Imlay, and became pregnant with her first daughter, Fanny. As a lone mother, she was a social outcast but went on to publish perhaps one of her greatest works, Letters Written in Sweden, Norway and Denmark.

Her daughter also suffered as both a lover and a mother. After she eloped with Shelley, aged 16, William Godwin mysteriously cut her off for many years, despite constantly appealing to Shelley for funds. The young couple lived in a kind of personal and artistic idyll in Italy for several years but the deaths of three of their four children precipitated spells of disabling depression in Mary and sparked Percy’s serial infatuations with other women. Mary’s stepsister Claire, who had a daughter with Byron, whose cruel treatment led to the child’s early death, wrote at the end of her life that the great Romantic experiment in free love had benefited only the men and crushed the women.

Both women’s stories are full of enriching paradox. Wollstonecraft, an ardent advocate of independence and freedom, was often a dependent and desperate lover but was able, eventually, to find happiness with Godwin, whom Gordon portrays as pernickety but passionate, brave but rather unkind. Mary Shelley was a highly gifted writer but, after her husband’s premature death by drowning a large part of her life was devoted to consolidating his literary reputation. Both women endured lengthy periods of depression, yet somehow always found a way to carry on writing.

Neither woman’s literary achievements were recognised during the 19th century, such was the whiff of personal scandal that still clung to their names. Wollstonecraft was not helped by Godwin’s decision, possibly for financial reasons, to rush out an ill-judged, partial and overly personal memoir of her soon after her death. And it was not until Muriel Spark’s critical biography of Mary Shelley, first published in 1951, claiming her as the founder of modern science fiction and a greater novelist than had been previously recognised, that interest in her writing revived. Second-wave feminist scholars finally rehabilitated the work and life of Wollstonecraft.

Charlotte Gordon has managed to produce that rare thing, a work of genuinely popular history. Her weaving together of the two lives – alternating short chronological slices, so that mother and daughter age together despite the decades that separate them – works beautifully.

More subtly, the book demonstrates the highly complex threads of political and personal inheritance at work in this poignant relationship. Mary Shelley was the daughter of two extraordinary people but she was also a remarkable and distinctive woman in her own right, inheriting her parents’ unusual drive and political values.

Her elder sister, Fanny – Wollstonecraft’s daughter by Imlay – tragically committed suicide at the age of 22. It is Mary Shelley’s bravery, emotional authenticity and commitment to her intellect, rather than any interest in status, social respectability or second-hand grandeur, that saved her again and again.

Romantic Outlaws: the Extraordinary Lives of Mary Wollstonecraft and Mary Shelley

Charlotte Gordon

Hutchinson, 649pp, £25