Larry Mendte admitted that he illegally viewed hundreds of Alycia Lane's e-mails from March 2006 to May 2008, at a time when leaked information about her personal life contributed to her downfall.
Mendte and Lane co-anchored evening broadcasts together for four years at KYW-TV, the CBS affiliate in Philadelphia, until Lane's arrest in December after an.
Months later, Mendte was fired and charged by federal prosecutors. His attorney, Michael Schwartz, has said Mendte cooperated from the start.
Mendte faces a maximum possible sentence of five years in prison but is likely to get much less under federal guidelines when he is sentenced Nov. 24. Prosecutors have agreed not to recommend any sentence.
Mendte declined to comment after his plea.
Prosecutors say Mendte accessed three of Lane's e-mail accounts from home and work more than 500 times between January and May of this year alone. Lane's attorney believes he acted out of jealousy.
The allegations are the latest embarrassment for the station, which had been making gains with the Mendte-Lane duo against longtime news leader WPVI-TV, the ABC affiliate.
Mendte, 51, was fired in June after FBI agents searched his home and seized his computer.
According to the criminal information filed in July, Mendte relayed details about Lane's criminal case and other information to a Philadelphia Daily News reporter.
Lane was also fired. She is suing the station over her dismissal, which the station said was necessary because she had become the subject of several news stories.
New York prosecutors in February downgraded felony charges that Lane struck the officer. A judge pledged to drop the remaining charges in August if she is not arrested again.
Mendte, who is married to local Fox news anchor Dawn Stensland, joined the station in July 2003 after several years at the local NBC affiliate. He previously co-hosted "Access Hollywood" and worked at stations in Chicago, San Diego and New York.