Mary Shelley's mother, Mary Wollstonecraft, died from infection eleven days after giving birth to her. Shelley grew close to her father, William Godwin, having never known her mother. Godwin hired a nurse, who briefly cared for her and her half sister, before marrying his second wife Mary Jane Clairmont, who did not like the close bond between Shelley and her father. The resulting friction caused Godwin to favour his other children.

Shelley's father was a famous author of the time, and her education was of great importance to him, although it was not formal. Shelley grew up surrounded by her father's friends, writers, and persons of political importance, who often gathered at the family home. This inspired her authorship at an early age. Mary, at the age of sixteen, met Percy Bysshe Shelley (who later became her husband) while he was visiting her father. Godwin did not approve of the relationship between his daughter and an older, married man, so they fled to France along with her stepsister, Claire Clairmont. On 22 February 1815, Shelley gave birth prematurely to her first child, Clara, who died two weeks later.

In the summer of 1816, Mary, Percy, and Claire took a trip to visit Claire's lover, Lord Byron, in Geneva. Poor weather conditions, more akin to winter, forced Byron and the visitors to stay indoors. To help pass time, Byron suggested that he, Mary, Percy, and Byron's physician, John Polidori, have a competition to write the best ghost story to pass time stuck indoors. Mary was just eighteen years old when she won the contest with her creation of Frankenstein.

Shelley's work was heavily influenced by that of her parents. Her father was famous for Enquiry Concerning Political Justice and her mother famous for A Vindication of the Rights of Woman. Her father's novels also influenced her writing of Frankenstein. These novels included Things as They Are; or, The Adventures of Caleb Williams, St. Leon, and Fleetwood. All of these books were set in Switzerland, similar to the setting in Frankenstein. Some major themes of social affections and the renewal of life that appear in Shelley's novel stem from these works she had in her possession. Other literary influences that appear in Frankenstein are Pygmalion et Galatée by Mme de Genlis, and Ovid, with the use of individuals identifying the problems with society. Ovid also inspires the use of Prometheus in Shelley's title.

The influence of John Milton's Paradise Lost and Samuel Taylor Coleridge's The Rime of the Ancient Mariner are evident in the novel. In The Frankenstein of the French Revolution, author Julia Douthwaite posits that Shelley probably acquired some ideas for Frankenstein's character from Humphry Davy's book Elements of Chemical Philosophy, in which he had written that,

science has ... bestowed upon man powers which may be called creative; which have enabled him to change and modify the beings around him ...

References to the French Revolution run through the novel; a likely source is François-Félix Nogaret [fr]'s Le Miroir des événemens actuels, ou la Belle au plus offrant (1790), a political parable about scientific progress featuring an inventor named Frankésteïn, who creates a life-sized automaton.

Both Frankenstein and the monster quote passages from Percy Shelley's 1816 poem, "Mutability", and its theme of the role of the subconscious is discussed in prose. Percy Shelley's name never appeared as the author of the poem, although the novel credits other quoted poets by name. Samuel Taylor Coleridge's poem "The Rime of the Ancient Mariner" (1798) is associated with the theme of guilt and William Wordsworth's "Tintern Abbey" (1798) with that of innocence.

Many writers and historians have attempted to associate several then-popular natural philosophers (now called physical scientists) with Shelley's work because of several notable similarities. Two of the most noted natural philosophers among Shelley's contemporaries were Giovanni Aldini, who made many public attempts at human reanimation through bio-electric Galvanism in London, and Johann Konrad Dippel, who was supposed to have developed chemical means to extend the life span of humans. While Shelley was aware of both of these men and their activities, she makes no mention of or reference to them or their experiments in any of her published or released notes.

Ideas about life and death discussed by Percy and Byron were of great interest to scientists of that time. They discussed ideas from Erasmus Darwin and the experiments of Luigi Galvani as well as James Lind. Mary joined these conversations and the ideas of Darwin, Galvani and perhaps Lind were present in her novel.

Shelley's …

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During the rainy summer of 1816, the "Year Without a Summer", the world was locked in a long, cold volcanic winter caused by the eruption of Mount Tambora in 1815. Mary Shelley, aged 18, and her lover (and future husband), Percy Bysshe Shelley, visited Lord Byron at the Villa Diodati by Lake Geneva, in Switzerland's Alps. The weather was too cold and dreary that summer to enjoy the outdoor holiday activities they had planned, so the group retired indoors until dawn.

Sitting around a log fire at Byron's villa, the company amused themselves by reading German ghost stories translated into French from the book Fantasmagoriana. Byron proposed that they "each write a ghost story." Unable to think of a story, Mary Shelley became anxious. She recalled being asked "Have you thought of a story?" each morning, and every time being "forced to reply with a mortifying negative." During one evening in the middle of summer, the discussions turned to the nature of the principle of life. "Perhaps a corpse would be re-animated," Mary noted, "galvanism had given token of such things". It was after midnight before they retired and, unable to sleep, she became possessed by her imagination as she beheld the "grim terrors" of her "waking dream".

I saw the pale student of unhallowed arts kneeling beside the thing he had put together. I saw the hideous phantasm of a man stretched out, and then, on the working of some powerful engine, show signs of life, and stir with an uneasy, half vital motion. Frightful must it be; for supremely frightful would be the effect of any human endeavour to mock the stupendous mechanism of the Creator of the world.

In September 2011, astronomer Donald Olson, after a visit to the Lake Geneva villa the previous year and inspecting data about the motion of the moon and stars, concluded that her "waking dream" took place between 2 a.m. and 3 a.m. on 16 June 1816, several days after the initial idea by Lord Byron that they each write a ghost story.

Mary Shelley began writing what she assumed would be a short story, but with Percy Shelley's encouragement, she expanded the tale into a fully-fledged novel. She later described that summer in Switzerland as the moment "when I first stepped out from childhood into life." Shelley wrote the first four chapters in the weeks following the suicide of her half-sister Fanny. This was one of many personal tragedies that impacted Shelley's work. Shelley's first child died in infancy, and when she began composing Frankenstein in 1816, she was probably nursing her second child, who was also dead by the time of Frankenstein's publication. Shelley wrote much of the book while residing in a lodging house in the centre of Bath in 1816.

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