Julian Assange spent his youth in Australia during the 1980s in a state of chaotic, perpetual motion. He moved more than two dozen times, bounced from school to school and was thrust, for a time, into what he called a New Age cult, before settling in Melbourne.

It was there, at age 16, that he adopted a calling: hacking. It would eventually place him on the edge of global disruption in an era of backlash against the national security and political establishments.

Mr. Assange, the 52-year-old founder of WikiLeaks, boarded a private jet this week from London for the long flight to a U.S. courtroom in Saipan, where he pleaded guilty on Wednesday to a single count of illegally obtaining and disseminating national security information.

A brief proceeding in a remote outpost capped a long legal saga.

For a case that attracted a spotlight for more than a decade, its final throes played out quickly and in relative obscurity.

Mr. Assange, wearing a black suit, offered his plea in a federal court in Saipan, the capital of the U.S. commonwealth of the Northern Mariana Islands in the Western Pacific. He had refused to appear in court on the U.S. mainland and asked that the hearing be at the remote judicial outpost, which is near his native Australia.

He responded carefully to questions from U.S. District Judge Ramona Manglona and defended his actions, describing himself as a journalist seeking information from sources, a task he said he saw as 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.”

Shortly after his plea, Judge Manglona sentenced him to time he had already served at Belmarsh Prison in Britain.

Mr. Assange is returning to Australia.

After his plea and sentencing, Mr. Assange boarded a plane for Australia, where he was expected to arrive in the capital, Canberra.

There is at least one more debt to pay: $520,000 to the Australian government for the chartered flight home, an amount he hopes to raise through crowdsourcing.

It is unclear what Mr. Assange, who had bouts of depression and a small stroke during his imprisonment, will do next.

But in Australia, relatives, supporters and politicians seemed eager to welcome him home. Kevin Rudd, the Australian ambassador to the United States, accompanied him at his court appearance in Saipan, and Prime Minister Anthony Albanese had lobbied for his release.

And Mr. Assange will be free to move around again, ending a period of confinement that lasted about a dozen years, first in self-exile in the Ecuadorean Embassy in London, then in prison after he had been indicted in the United States and taken into custody by British authorities.

He was an audacious teenage hacker.

If the past is any guide, Mr. Assange may not remain idle for long.

By his late teens, Mr. Assange was, by his own account, the most accomplished hacker in Australia, claiming to have breached thousands of systems, from a local telecommunications commission to servers at the Pentagon, using the alter ego Mendax, among other aliases. (As a teenager, he adopted the credo “splendide mendax,” Latin for “brilliantly untruthful.”)

Mr. Assange has said his goal has always been to publicly share important information hidden by big government and big business, without damaging the systems he infiltrated. And by the early 1990s, Mr. Assange and a group of hackers began to systematically target systems run by what he called “the U.S. military-industrial complex.”

In 1994, he had his first serious brush with the law, facing a 31-count indictment for hacking into servers owned by Telecom Australia. Mr. Assange, who faced 290 years in prison, fell into a deep depression, wandering around the wilderness near Melbourne and sleeping outdoors.

Eventually, he entered a guilty plea and received no jail time. But the experience was a searing ordeal and steeled his political resolve to attack institutions he believed were infringing on individual liberties, including the U.S. National Security Agency.

WikiLeaks cast itself as a beacon of transparency.

Mr. Assange and a group of like-minded activists, hackers, programmers and academics founded WikiLeaks in 2006, with the stated mission of shattering the veil of secrecy protecting powerful cabals in private and public life. He defined his role as a digital Robin Hood, freeing “persecuted documents” from captivity in secret computer networks.

In its early years, WikiLeaks worked closely with mainstream news organizations, uncovering details of extrajudicial killings in Kenya, China’s repression of dissidents, and possible financial corruption in the U.S. and Peru, among many others.

The group’s success made its founder famous. Mr. Assange was tireless, brash and itinerant, traveling from country to country to recruit volunteers, court would-be leakers and herald the virtues of extreme institutional transparency.

As the 2010s dawned, Mr. Assange increasingly set his sights on the United States, which would earn him simultaneous worldwide acclaim as a free-speech warrior and, ultimately, a half-decade behind English bars.

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

He was repeatedly on the run.

At the time, Mr. Assange was already on the run, heading to London after the Swedish authorities charged him with sexual assault. (He has denied the charges, saying they were a backdoor attempt to extradite him to the United States. The case was dropped in late 2019.)

In 2012, Mr. Assange was granted asylum by Ecuador, and moved into a 300-square-foot space in the country’s embassy in London.

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.

By this time, Mr. Assange had worn out his welcome. He was taken into custody by the British police and transferred to Belmarsh, where he was confined to a cell for 23 hours a day. According to an account published in The Nation this year, he ate his meals off a tray alone, surrounded by 232 books and allowed only an hour a day for exercise in a prison yard.

A secret hearing paved the way for his release.

In the end, the choreographed multinational dance that led to his release took place behind closed doors, at a secret bail hearing in London last Thursday, British officials said.

While many of Mr. Assange’s supporters lamented the requirement that he plead guilty to any crime, he seemed relieved just to be free, if the images posted by his wife and friends on social media are any guide.

He is, at least, back in motion