Julian Assange, the founder of WikiLeaks, agreed to plead guilty on Monday to a single felony count of illegally obtaining and disclosing national security material in exchange for his release from a British prison, ending his long and bitter standoff with the United States.

Mr. Assange, 52, was granted his request to appear before a federal judge at one of the more remote outposts of the federal judiciary, the courthouse in Saipan, the capital of the Northern Mariana Islands, according to a brief court filing made public late Monday. He is expected to be sentenced to about five years, the equivalent of the time he has already served in Britain, according to a law enforcement official familiar with the terms of the agreement.

It was a fitting final twist in the case against Mr. Assange, who doggedly opposed extradition to the U.S. mainland. The islands are a United States commonwealth in the middle of the Pacific Ocean — and much closer to Mr. Assange’s native Australia, where he is a citizen, than courts in the continental United States or Hawaii.

Shortly after the deal was disclosed, WikiLeaks said that Mr. Assange had left London. Mr. Assange is scheduled to appear in Saipan at 9 a.m. local time on Wednesday and is expected to fly back to Australia “at the conclusion of the proceedings,” Matthew J. McKenzie, an official in the Justice Department’s counterterrorism division, wrote in a letter to the judge in the case.

Early on Tuesday morning, his wife, Stella Assange, posted a video of her husband signing paperwork and boarding a plane on Monday.

Barring last-minute snags, the deal would bring to an end a prolonged battle that began after Mr. Assange became alternately celebrated and reviled for revealing state secrets in the 2010s.

Those included material about American military activity in Iraq and Afghanistan, as well as confidential cables shared among diplomats. During the 2016 campaign, WikiLeaks released thousands of emails stolen from the Democratic National Committee, leading to revelations that embarrassed the party and Hillary Clinton’s campaign.

In 2019, a federal grand jury indicted Mr. Assange on 18 counts related to WikiLeaks’ dissemination of a broad array of national security documents. Those included a trove of materials sent to the organization by Chelsea Manning, a former U.S. Army intelligence analyst who handed over information about military planning and operations nearly a decade earlier.

If convicted, Mr. Assange could have faced a maximum of 170 years in a federal prison. Until Monday evening, Mr. Assange had been held in Belmarsh, one of Britain’s highest-security prisons, in southeast London.

Mr. Assange was confined to a cell for 23 hours a day, eating his meals off a tray alone, surrounded by 232 books and allowed only an hour a day for exercise in a prison yard, according to an account published in The Nation this year.

When asked about his pallor, Mr. Assange — who has not been able to walk outside unsupervised for more than a decade — joked, “They call it prison pale.”

His release was not unexpected. Earlier this year, Prime Minister Anthony Albanese of Australia suggested that U.S. prosecutors needed to conclude the case, and President Biden signaled that he was open to a rapid resolution. Top officials at the Justice Department accepted an agreement with no additional prison time because Mr. Assange had already served longer than most people charged with a similar offense — in this case, over five years in prison in Britain.

Soon after the charges were unsealed in 2019, the London Metropolitan Police entered Ecuador’s embassy, where Mr. Assange had sought sanctuary years earlier to avoid extradition to Sweden, where he faced accusations of sexual assault. He has been held in custody ever since, as his legal team has fought the Justice Department’s efforts to extradite him.

After weeks of negotiations, Mr. Assange is pleading guilty to one of the charges in the indictment — conspiracy to disseminate national defense information — which carries a sentence of up to 10 years in prison.

Mr. Assange and his supporters have long argued that his efforts to obtain and publicly release sensitive national security information was in the public interest, and deserved the same First Amendment protections afforded to investigative journalists.

Many of Mr. Assange’s supporters renewed those concerns even as they expressed relief that he would be released.

“The United States has now, for the first time in the more than 100-year history of the Espionage Act, obtained an Espionage Act conviction for basic journalistic acts,” said David Greene, director of the Electronic Frontier Foundation Civil Liberties, a nonprofit focused on First Amendment issues.

“These charges should never have been brought,” he said.

In 2021, a coalition of civil-liberties and human-rights groups urged the Biden administration to drop its efforts to extradite him from Britain and prosecute him, calling the case “a grave threat” to press freedom.

Much of the conduct he is accused of is what “journalists engage in routinely,” the group contended. “News organizations frequently and necessarily publish classified information in order to inform the public of matters of profound public significance.”

But U.S. officials argued that Mr. Assange’s actions went far beyond news gathering, putting at risk national security. The material furnished by Ms. Manning, prosecutors claimed, endangered the lives of service members and Iraqis who worked with the military, and made it harder for the country to counter external threats.

Mr. Assange has remained in Belmarsh as he has repeatedly challenged the order for his removal. Last month, Mr. Assange won a bid to appeal the extradition order.

Afterward, Ms. Assange, who married Mr. Assange after joining his legal team fighting extradition efforts to Sweden, told supporters gathered outside the central London court that the case should be abandoned.

“The Biden administration should distance itself from this shameful prosecution,” said Ms. Assange, who secretly began a relationship with Mr. Assange when he was living in the Ecuadorean embassy. The pair have two young sons.

Mr. Assange has rarely been seen in public as his case has wound its way through the courts, citing health issues. In 2021, Mr. Assange had a small stroke while in prison. He did not attend the hearing in May because of undisclosed health reasons.

Ms. Assange, in another video posted to social media early Tuesday, which was recorded outside of Belmarsh Prison last week, said that developments had been occurring very quickly.

“This period of our lives, I am confident now, has come to an end,” she said. She added, “What starts now, with Julian’s freedom, is a new chapter.”