Assange was granted permission by the High Court of London to appeal the case to U.K. Supreme Court. The Supreme Court must accept the case before it can proceed.
Stella Moris, Assange's fiancée, stated outside the courthouse that "Make no mistake, today we won in court", noting that Assange remains in London's Belmarsh Prison.
She added, "We will fight it until Julian is free."
According to the court's website, the Supreme Court usually takes eight weeks to hear an appeal.
This is the latest in Assange’s long struggle to avoid a U.S. trial on a number of charges related WikiLeaks’ publication of classified documents more that a decade ago.
A London district court judge rejected an extradition request from the United States. He argued that Assange would likely die in harsh U.S. prison conditions. Later, U.S. authorities assured Assange that he wouldn't be subject to the extreme treatment his lawyers claimed would threaten his mental and physical health.
Last month, the High Court overturned the decision of the lower court by stating that Assange was guaranteed humane treatment because the U.S. promises had been sufficient.
These assurances were the main focus of Monday's High Court ruling.
Assange's lawyers want to appeal the fact that the U.S. offered assurances following the lower court's ruling. The High Court overturned the ruling of the lower court, stating that the judge should have allowed the U.S. to offer assurances before making her final decision.
Assange was granted permission by the High Court to appeal, so that the Supreme Court can decide "in which circumstances an appellate court can receive assurances from one requesting state... in extradition proceedings."
Assange's lawyers argued that the U.S. government’s promise that Assange will not be subject to extreme conditions was meaningless as it is conditional and can be modified at the discretion American authorities.
The U.S. requested British authorities to extradite Assange to face 17 charges of espionage as well as one charge of computer misuse in connection to WikiLeaks' publication a number of diplomatic and military documents.
Assange, 50 years old, is currently being held at Belmarsh Prison. He was originally arrested in 2019 for failing to pay bail during a separate legal battle. He spent seven years in London's Ecuador Embassy before that. Assange requested protection at the Embassy in 2012 to avoid being extradited to Sweden for rape and sexual assault allegations.
Sweden ended its investigation into sex crime in November 2019, owing to the lack of time.
American prosecutors claim that Assange illegally assisted Chelsea Manning, U.S. Army intelligence analyst, to steal classified diplomatic cables. WikiLeaks published the files later on, putting lives at stake.
Assange lawyers argue that Assange should not have been charged as he was acting as journalist. The First Amendment to the U.S. Constitution, which guarantees freedom of expression, protects Assange. According to them, the documents he published revealed U.S. military wrongdoings in Iraq and Afghanistan.
Barry Pollack, the United States attorney for Barry Pollack said that he should not be subject to criminal prosecution or decades in prison for publishing truthful information.