Lynn Picknett (born 1947) is an English writer of books that are mainly about religious history and popular conspiracy theories, the paranormal, the occult, and historical mysteries.Born in Folkestone, Kent, England, in April 1947, Picknett grew up in an alleged haunted house in York, attending Park Grove Junior School and Queen Anne Grammar School. After graduating from university with an Upper 2nd (hons) degree in English Literature, she briefly became a teacher, a shop assistant, and a stand-up comic before moving to London in 1971 to join Marshall Cavendish Publications as a trainee sub-editor.

In 1990, Picknett was guest curator for the Royal Photographic Society's exhibition The Unexplained at Bath, performing the same function in 1999 for the National Museum of Photography, Film and Television at Bradford.

In the early 1990s, Picknett teamed up with fellow researcher and writer Clive Prince. Their first book, Turin Shroud: How Leonardo da Vinci Fooled History, claimed that the characteristics of the Shroud of Turin could be reproduced using only a pinhole camera (camera obscura) and that Leonardo da Vinci, in producing the image, used his own face for the model of Jesus. This is inconsistent with the first exhibition of the Shroud of Turin, authentic or not, which was in 1357, almost a century before the birth of da Vinci, although Picknett and Prince counter-argue that the relic predating da Vinci "was not the same one as today's."

The 1997 book The Templar Revelation by Picknett and Prince was credited by Dan Brown, both in The Da Vinci Code and in the 2006 court case (Baigent & Leigh v Random House), as the main inspiration for his novel.