Before Fowles published The French Lieutenant's Woman in 1969, he had already established his literary reputation with his novels The Collector (1963) and The Magus (1965). While writing The French Lieutenant's Woman, he was working on the screenplay for the film adaptation of The Magus. Moreover, The Collector had already been adapted in a 1965 film that gained Fowles further popular attention.
Fowles described his main inspiration for The French Lieutenant's Woman to be a persistent image of a 'Victorian Woman,' who later developed into the novel's titular character Sarah Woodruff. In a 1969 essay titled "Notes on an Unfinished Novel," Fowles reflects on his writing process. He said he had an image during the autumn of 1966 of "A woman [who] stands at the end of a deserted quay and stares out to sea." He determined that she belonged to a "Victorian Age" and had "mysterious" and "vaguely romantic" qualities. He made a note at the time about the function of the novel, saying
You are not trying to write something one of the Victorian novelists forgot to write; but perhaps something one of them failed to write. And: Remember the etymology of the word. A novel is something new. It must have relevance to the writer's now - so don't ever pretend you live in 1867; or make sure the reader knows it's a pretence."
In an appended comment, dated "October 27, 1967", he writes that he finished the first draft of the novel at about 140,000 words.
Throughout the essay, Fowles describes multiple influences and issues important to the novel's development, including his debt to other authors such as Thomas Hardy. In the essay, he describes surprise that the female character Sarah had taken the primary role in the novel. Later Fowles described other influences shaping the characters development, noting that the characters and story of The French Lieutenant's Woman were loosely derived from Claire de Duras's 1823 novel Ourika, which features a tragic affair between an African woman and French military man. Fowles later published a 1977 translation of Ourika into English.