In his ruling, Judge Paul Innes of State Superior Court said the messages were public records.
The decision is a blow to Mr. Corzine, who wanted to keep private the e-mail messages he exchanged with Carla Katz, a former companion, during state worker contract talks in 2006 and 2007.
“The relationship created a clear potential for conflict,” Judge Innes wrote. “These types of communications would be the sort of communications the Supreme Court felt the public had the right of access to understand and evaluate the reasonableness of the public body’s actions.”
Tom Wilson, the New Jersey Republican Party chairman, sued to make the e-mail messages public, contending that the personal relationship could have affected negotiations.
Mr. Corzine, a Democrat, contends that the e-mail messages are private under privileges accorded governors.