The Shelleys left Britain in 1818 for Italy, where their second and third children died before Shelley gave birth to her last and only surviving child, Percy Florence Shelley. In 1816, the couple and Mary's stepsister famously spent a summer with Lord Byron and John William Polidori near Geneva, Switzerland, where Shelley conceived the idea for her novel Frankenstein. They married in late 1816, after the suicide of Percy Shelley's first wife, Harriet. Over the next two years, she and Percy faced ostracism, constant debt and the death of their prematurely born daughter. Upon their return to England, Mary was pregnant with Percy's child. Together with her stepsister, Claire Clairmont, she and Percy left for France and travelled through Europe. In 1814, Mary began a romance with one of her father's political followers, Percy Bysshe Shelley, who was already married. When she was four, her father married a neighbour, Mary Jane Clairmont, with whom Mary came to have a troubled relationship. She was raised by her father, who provided her with a rich if informal education, encouraging her to adhere to his own anarchist political theories. Mary's mother died less than a fortnight after giving birth to her. Her father was the political philosopher William Godwin and her mother was the philosopher and women's rights advocate Mary Wollstonecraft.

She also edited and promoted the works of her husband, the Romantic poet and philosopher Percy Bysshe Shelley. Mary Wollstonecraft Shelley ( UK: / ˈ w ʊ l s t ən k r ɑː f t/ née Godwin 30 August 1797 – 1 February 1851) was an English novelist who wrote the Gothic novel Frankenstein or, The Modern Prometheus (1818), which is considered an early example of science fiction and one of her best-known works.

William Godwin the Younger (half-brother).

Mary wollstonecraft shelley