Harriet Deborah Vane, later Lady Peter Wimsey, is a fictional character in the works of British writer Dorothy L. Sayers (1893–1957) and the sequels by Jill Paton Walsh.

Vane, a mystery writer, initially meets Lord Peter Wimsey while she is on trial for poisoning her lover (Strong Poison). The detective falls in love with her and proposes marriage, but she refuses to begin a relationship with him, traumatised as she is by her dead lover's treatment of her and her recent ordeal. In Have His Carcase, she collaborates with Wimsey to solve a murder but still finds him too cold and distant. She eventually returns his love (Gaudy Night) and marries him (Busman's Honeymoon).

Harriet Vane was born in 1903, the only daughter of a country doctor. She was an undergraduate at Shrewsbury College, Oxford (based on Sayers' own Somerville College, the location of which is given as the Balliol College Sports Grounds, now partly occupied by a residential annexe, on Holywell Street) and took a First in English. Her parents both died while she was quite young and she was left to make her own fortune at the age of 23. She has had some success as a writer of detective stories, living and socialising with other artists in Bloomsbury. She begins a relationship with Philip Boyes, a more literary but far less successful writer who professes not to believe in marriage, and she agrees to live with him without marrying. After a year of this arrangement, Boyes believes that she truly loves him and proposes marriage. Angered by his hypocrisy and aghast at being offered marriage as "a bad-conduct prize", Harriet breaks off the relationship.

Boyes dies soon afterwards of arsenic poisoning – the method Harriet had researched for her new book. She is arrested and tried for murdering Boyes. Wimsey comes to her rescue by proving who really poisoned Boyes.

After Harriet is acquitted, she remains quite notorious. Sales of her books skyrocket. Wimsey continues to pursue her romantically, but Harriet repeatedly declines marriage on the principle that gratitude is not a good basis for it. To relax, she takes a walking tour, during which she finds a corpse on a beach, adding to her notoriety. The press is naturally interested; Wimsey hastens to the scene, after receiving a tip from a journalist friend, to help shield Harriet from suspicion. The two investigate the death (when they are not romantically sparring) and unmask the murderer.

A few years later, in 1935, Harriet returns to her old Oxford college for a reunion (or Gaudy) and is later asked to investigate some strange occurrences there. She protests that she is not a sleuth, and recommends that the college hire professional detectives. However, failing to reach either Miss Climpson, at the female detective agency set up by Wimsey, or Wimsey himself, she agrees to assist the college. Her cover is research into Sheridan Le Fanu (in the books spelled Lefanu), an Anglo-Irish writer of Gothic tales and mystery novels of the 19th century. (In Thrones, Dominations, the Authors' Note – plural, since the novel was finished posthumously by another author – states that Vane published a monograph on Le Fanu in 1946.) After months of unpleasant incidents at the college and with no solution in sight, Harriet turns once again to Wimsey for help. By the end of the book the villain has been discovered and Harriet has finally accepted Wimsey's proposal.

The press is delighted to have a woman once accused of murder engaged to a duke's son, and happily publicises the fact. Wimsey and Vane have a quiet wedding in Oxford with no notice to the press, and escape to their new country residence, Talboys, a Tudor farmhouse in North Hertfordshire which Harriet had admired as a child and which Peter has given her as a wedding present. The body of the former owner is discovered in the cellar, leading them to investigate.

Thrones, Dominations, a novel abandoned by Sayers and finished by Jill Paton Walsh, is set in and around London, shortly after Wimsey and Vane return from their honeymoon.