The lawsuit was filed Friday in federal court in Manhattan, the legal news website Law360 reported. In the complaint, Lee, now 87, alleges Samuel Pinkus took advantage of her condition while she was recovering from a stroke in 2007 to get her to hand him the rights to the novel.
The novel, published in 1960, won a Pulitzer Prize and has sold millions of copies. It was made into a film, starring Gregory Peck in an Oscar-winning performance as the small-town southern lawyer Atticus Finch.
Lee never published another book and lived quietly, avoiding the public eye.
In the complaint, Lee suggests her troubles began in 2002 when Pinkus allegedly took over the clients of McIntosh & Otis, owned by his father-in-law. Five years later, Lee said, she was duped into assigning Pinkus' company, Veritas Media Inc., the rights to her book.
Veritas is also a defendant.
"Through all these years, Pinkus ignored his agent's duty of loyalty and diligence to Harper Lee, his principal, and neglected his obligation to act at all times in her interest," the complaint said.