Julian Assange, the founder of WikiLeaks, pleaded guilty on Wednesday to a felony charge of violating the U.S. Espionage Act, securing his freedom under a plea deal that saw its final act play out in a remote U.S. courtroom in Saipan in the Western Pacific.

He appeared in court wearing a black suit with his lawyer, Jennifer Robinson, and Kevin Rudd, the Australian ambassador to the United States. He stood briefly and offered his plea more than a decade after he obtained and published classified secret military and diplomatic documents in 2010, moving a convoluted case involving several countries and U.S. presidents closer to its conclusion.

After a few hours of proceedings, he boarded a plane for Australia, where he was expected to arrive in the capital, Canberra, shortly before 8 p.m.

It was all part of an agreement allowing Mr. Assange to return to normal life after spending more than five years in British custody — most of it fighting extradition to the United States.

His family and lawyers documented his journey from London to Bangkok and on to Saipan, capital of the Northern Mariana Islands, a U.S. commonwealth, posting photos and videos online from a chartered jet. His defense team said that in the negotiations over his plea deal, Mr. Assange had refused to appear in a court on the U.S. mainland, and that he had not been allowed to fly commercial.

His wife, Stella, posted an urgent fund-raising appeal on the social media platform X, seeking help in covering the $520,000 cost of the flight, which she said would have to be repaid to the Australian government. She also wrote on X that watching a video of Mr. Assange entering the courtroom made her think of “how overloaded his senses must be, walking through the press scrum after years of sensory deprivation and the four walls of his high-security Belmarsh prison cell.”

In court, Mr. Assange responded carefully to questions from U.S. District Judge Ramona Manglona, who was appointed by former President Barack Obama. He defended his actions, describing himself as a journalist seeking information from sources, a task he said he saw as legal and constitutionally protected.

“I believe the First Amendment and the Espionage Act are in contradiction with each other,” he said, “but I accept that it would be difficult to win such a case given all the circumstances.”

In Australia, relatives, supporters and politicians seemed eager to welcome Mr. Assange home.

Prime Minister Anthony Albanese had lobbied heavily for his release. He responded to the deal by noting that the case had “dragged on for too long.” Many Australians seemed to agree, noting that Chelsea Manning, the person who had passed a vast trove of documents to WikiLeaks — including hundreds of thousands of military incident reports from Afghanistan — had already served her sentence and been set free.

Despite Australia’s own strict espionage laws and deeply entrenched culture of secrecy — which would most likely have ensured many years in prison had his leaks focused on the Australian government — his return won support from politicians on both the left and right.

David Shoebridge, a Greens senator from Sydney known for seeking to legalize cannabis, posted a video on X saying that Mr. Assange “should never have been in jail for the crime of telling the truth.”

Barnaby Joyce, a conservative rural lawmaker, was just as effusive.

“I was very happy to hear that an Australian citizen, who never committed a crime in Australia, was not a citizen of the United States, was never charged in the United Kingdom, is coming home,” he said.

The embrace of Mr. Assange reflects what many see as both a cultural affinity for the underdog and a degree of ambivalence about America’s wars after the Sept. 11 attacks, and the U.S. justice system.

“For those at the liberal end of the spectrum, he is a hero precisely because he revealed secrets that Washington wanted to hide,” said Hugh White, a former Australian government defense official and now a professor of strategic studies at the Australian National University.

“Even conservative Australians,” he added, “are not as unwilling as our public rhetoric might suggest to disapprove of what Washington does.”

Mr. Assange’s father, John Shipton, said that having his son home after 15 years of distance and detention incarceration in one form or another was “pretty good news.”