The WikiLeaks founder walked out of a U.S. courthouse in the remote island of Saipan a free man, after pleading guilty to violating the Espionage Act by publishing U.S. military secrets. Photo: Chung Sung-Jun/Getty Images

Assange’s family said the breakthrough happened when it became clear he would be able to raise First Amendment arguments at an appeal hearing in the U.K. The U.S. also turned sympathetic to arguments made by Australia that Assange’s detention had gone on too long, and it was time for legal proceedings to end and him to come home.

Australian Prime Minister Anthony Albanese said he first raised the matter with President President Biden at a North Atlantic Treaty Organization summit in Madrid two years ago. A delegation of Australian politicians flew to Washington last year to advocate for Assange’s release.

“Quiet diplomacy was the way to go,” said Arthur Sinodinos, who was Australia’s ambassador to the U.S. from 2020 to 2023. “This was not the sort of issue to try and beat up the Americans on in public.”

Assange, 52, said Australia’s intervention was critical to his release. Assange told Albanese in a phone call after he landed in Canberra, Australia’s capital, that he had saved his life, one of his lawyers said.

Assange didn’t attend a press conference organized by WikiLeaks soon after his arrival on Wednesday night, or a media event on Thursday. His wife, Stella, said he needed time to heal. She said their children were so excited when they found out Assange would be coming home that they jumped on the sofa.

Assange, who said he was working as a journalist, remains a polarizing figure. To some he’s a hero for exposing wrongdoing and advocating for free speech and media freedom. Others argue he endangered national security at a time of war. The U.S., in bringing the legal proceedings, disputed that Assange was a journalist.

One issue that Assange and his supporters are set to pursue in the near term is a presidential pardon. His lawyers said the case should never have been brought, but it needed to end. A pardon, his supporters argue, would help unwind the damage done by his prosecution, which they say could have a chilling effect on journalists.

But a pardon is far from certain. Assange’s detention had become a sticking point between the U.S. and Australia, a close ally that has been deepening military cooperation with the U.S., and the leaders of both nations could be happy to let the matter rest now that Assange is free.

Galvanizing the global network of volunteers who had advocated for Assange’s release could also be a challenge, given that many are tired from years of effort and their main goal has been achieved. And there could be opposition from both sides of the aisle in the U.S., political analysts said.

Whether to issue a pardon is ultimately a personal decision by the president. A special office within the Justice Department evaluates requests for pardons and then provides recommendations.

Whatever the outcome of that campaign, Assange will find it hard to resist the temptation to talk about the issues that he cares about, people close to him say. Stella Assange said her husband will always defend human rights and speak out against injustice. One of his lawyers said Assange had sacrificed his own freedom for freedom of the press.

Assange also appears entrenched as WikiLeaks’s figurehead, even if it’s unclear how long it will take him to recover out of the public eye. He’ll be at a “hideout in the Australian bush,” according to Assange’s brother, Gabriel Shipton.

“He’ll always have an outsized voice,” Shipton said. “There will be quite a large demand for him to speak on different issues. And I’m sure he will oblige.”

In some ways, Assange’s development into a firebrand activist with scores of followers is at odds with a childhood where he struggled to fit in.

Assange moved around frequently during his youth, attending multiple schools. He was drawn to computers, with a lawyer once describing his computer as his only friend, and in the mid-1990s he pleaded guilty to hacking charges, according to a report published in an Australian newspaper. A young Assange, the report said, was “not afraid to speak up to authority.”

In 2006, he founded WikiLeaks, created as a haven for whistleblowers seeking to expose government secrets. In 2010, WikiLeaks released “Collateral Murder,” an edited video that showed a U.S. military helicopter in Iraq firing on a group of people who turned out to include journalists from Reuters. It provoked an international media sensation.

“I was a famous teenage hacker in Australia, and I’ve been reading generals’ emails since I was 17,” Assange said at an event in 2009, court documents show.

His legal troubles accelerated soon after. Assange initially faced allegations of rape in Sweden in 2010. He sought asylum in the Ecuadorean embassy in London in 2012 and holed up there for years, fathering two children.WikiLeaks published tens of thousands of classified documents, prompting U.S. prosecutors in 2019 to charge him under the U.S. espionage law. He was apprehended by U.K. law enforcement after being kicked out of the Ecuadorean embassy. The Swedish allegations were eventually dropped.

Human-rights activists and doctors were concerned about Assange’s treatment in prison. A U.N. representative and his medical team visited him in May 2019 and found that he was showing “all the symptoms typical for prolonged exposure to psychological torture,” the U.N. human-rights agency said.

In a post on X, Stella Assange said her husband suffered a stroke on the first day of a court hearing in October 2021. In the Lancet, a medical journal, a letter from doctors who supported Assange said he had been strip searched, handcuffed repeatedly and moved to multiple different holding cells. During legal proceedings, he was held in a bulletproof enclosure and unable to fully hear.

U.K. authorities denied Assange had been ill-treated in statements to media organizations.

“He’s just rediscovering normal life,” Stella Assange said Thursday. “And he needs space to do that.”

Write to Mike Cherney at mike.cherney@wsj.com