A former Pentagon counterterrorism analyst pleaded guilty on Thursday to sharing classified information with two journalists, one of whom was his girlfriend.

The former analyst, Henry Kyle Frese, 31, pleaded guilty in the United States District Court in eastern Virginia to willful transmission of top secret national defense information. He faces up to 10 years in prison when sentenced on June 18.

The conviction of Mr. Frese, who was arrested last October at his office at the Defense Intelligence Agency, represented a victory in the Justice Department’s aggressive campaign to crack down on illegal leaks of government information.

The case was prosecuted with a wiretap of Mr. Frese’s phone, perhaps the most intrusive tool in criminal investigators’ arsenal.