Michael Baigent and Richard Leigh are suing publisher Random House, claiming that Brown's "The Da Vinci Code" lifts ideas from their 1982 nonfiction book, "The Holy Blood and The Holy Grail." Their work explores theories that Jesus and Mary Magdalene married and had a child and that their blood line continues to the present day.
A similar theme is explored in Brown's novel, which has sold some 25 million copies around the world and is being made into a Hollywood movie starring Tom Hanks.
Lawyers for both sides met Thursday at London's High Court to agree on details of a trial, scheduled to start Feb. 27. They reached an agreement outside court on technical details of the case.
A spokesman for Random House said the parties had agreed that a "substantial part" of the claim would be dropped.
In August, a U.S. judge ruled that "The Da Vinci Code" does not infringe on the copyrights of a book published in 2000 by another author.
U.S. District Judge George B. Daniels said Dan Brown's book exploring codes hidden in Leonardo Da Vinci's artwork is not substantially similar to "Daughter of God," by Lewis Perdue, who had threatened to sue and demanded $150 million for perceived infringement.
Brown's book "is simply a different story," Daniels said.