Washington is eager to bring the 50-year-old Australian to justice in connection with the release of 500,000 secret military files from the US-led wars in Iraq and Afghanistan.
The High Court in London in December overturned a lower court’s decision not to send him to the United States because he was at risk of suicide.
But Assange’s lawyers challenged the decision, arguing that the highest court in the land should decide “legal questions of general public interest”.
“The defendant’s motion for a determination of law is granted,” Judges Ian Burnett and Timothy Holroyde said in a written judgment.
The judges said that while they did not grant him the right to appeal to the Supreme Court, Assange had the right to do so himself.
Now the Supreme Court must decide whether or not to accept the case.
Assange’s fiancée and mother of his two young children, Stella Moris, walked out of court smiling and visibly relieved.
“What happened in court today is exactly what we wanted,” she said.
“The current situation is that the Supreme Court must decide whether or not to hear the appeal. But don’t get me wrong, we won in court today.
“If there was justice, the crimes that Julian uncovered – war crimes, the killing of innocent civilians – would go unchallenged.
“Our fight continues. We will fight until Julian is free.”
Crowds gathered outside the Royal Courts of Justice in central London to applaud the decision.
“I am incredibly relieved,” said Sue Barnett, 61, of Nottingham, central England, holding up a placard which read: “10 years is enough. Free Assange now.
“We all feared the worst.
Assange could be imprisoned for up to 175 years in the United States, although the exact sentence is difficult to estimate.
WikiLeaks editor Kristinn Hrafnsson welcomed Monday’s verdict as a “partial victory” and called the US charges against Assange a “blatant terrorist attack on press freedom around the world”.
At a two-day hearing in October, US lawyers argued that a lower court judge failed to give enough weight to other expert testimony about Assange’s mental state.
They also pointed to diplomatic assurances given since the January decision that Assange would not be criminalized and adequately cared for in a supermax federal prison.
Two judges endorsed that appeal and accepted the new assurances, noting that they were not uncommon in such cases and that they were “solemn undertakings offered by one government to another”.
They ordered the case sent to Westminster Magistrates’ Court with instructions to send it to Home Secretary Priti Patel for the final say.
Assange has been held in London’s maximum-security Belmarsh prison since 2019 because he is considered a flight risk after he waived bail in 2012 over allegations he sexually assaulted two women in Sweden.
He spent seven years in the Ecuadorian embassy in London to avoid being deported to Sweden to face charges that were later dropped.
A coalition of anti-war groups and thousands of peace activists signed a statement on Friday calling for his immediate release.
Moris said he spent more time at Belmarsh than many prisoners convicted of violent crimes.
Nathan Fuller, director of the Courage Foundation, said: “As the Biden administration confronts American opponents about its press freedom shortcomings, it should come to grips with its own hypocrisy.
“Imprisoning Julian Assange for revealing the truth about America’s wars is an insult to all who fight for peace and human rights.”