Ms. Winner, who entered her plea in Federal District Court in Augusta, Ga., was arrested last June and accused of sharing a classified report about Russian interference in the 2016 election with the news media.

Ms. Winner, who is now 26, has been jailed since her arrest and wore an orange prison jumpsuit and white sneakers to the hearing. Her decision to plead guilty to one felony count allows the government both to avoid a complex trial that had been scheduled for October and to notch a victory in the Trump administration's aggressive pursuit of leakers.

"All of my actions I did willfully, meaning I did so of my own free will," Ms. Winner told Chief Judge J. Randal Hall on Tuesday. Throughout the hearing, Ms. Winner kept her hands behind her back while she answered questions about whether she understood the terms of the plea deal.