As a result of the Court of Appeal ruling, Michael Baigent and Richard Leigh are on the hook for millions of dollars in legal costs for their failed case against Random House, the publisher of both books, The Times of London said.
The high court said Brown did not co-opt the theme of the 1982 book "The Holy Blood and the Holy Grail," which Baigent and Leigh wrote with a third co-author.
A high court judge last year cleared Brown of copyright infringement of ideas set out in "The Holy Blood and the Holy Grail."
"The Holy Blood and the Holy Grail" theorizes that Jesus and Mary Magdalene married and had a child, and that their bloodline continues to modern day, with a secret society protecting their heirs against wicked conspiracies involving the Catholic Church. Brown's 2003 novel, which weaves a story around a similar theme, has earned him hundreds of millions of dollars.
Brown testified at the original trial but did not attend the appeal hearing.