Condit was accused by Dunne of withholding information from authorities about the slaying of Washington intern Chandra Levy in 2002, the New York Daily News reported Wednesday.
Condit's suit filed in U.S. District Court claims Dunne made comments on CNN's "Larry King Live" in November 2005 that inflicted on him "public hatred, contempt and ridicule," the suit said.
Just eight months after publicly apologizing to Condit and paying him an unknown sum of money, Dunne told the show's fill-in host Bob Costas, "I think (Condit) knows more about what did happen than he has ever said."
Condit is seeking more than $75,000 in compensatory damages and unspecified punitive damages.
The new lawsuit also quotes Dunne as saying Condit "knew that Levy was going to be killed."