In January, a British judge rejected an effort to extradite the 50-year-old, on the grounds that the risk of him taking his own life was very high if he was placed in the US prison system.
Yet in August, Britain’s high court gave permission to the US to appeal the decision, saying it was “at least arguable” the conclusion made in January had been wrong. The case will now be heard over two days at the high court in London.
On Monday, Stella Moris, Mr Assange’s partner and mother of two of his children, said she had seen the WikiLeaks’ founder in Belmarsh Jail on Saturday and she was shocked by his physical appearance.
“I saw Julian on Saturday morning in Belmarsh prison, and I was quite taken aback by how thin he was,” she said at a press conference.
“He was wearing a T-shirt. I haven’t seen his arms for a long time, so I could see how thin he’s got. He was looking very unwell.”
She added: “There have been such important developments in the case, over the past three months, I’d say that we both hope that this will be the end of it.”
Mr Assange founded WikiLeaks in 2006 and used it to highlight many incidents from the US’s so-called war on terror that he and his supporters considered war crimes.
Among the most high profile was video footage taken from inside one of two US AH-64 Apache helicopters in Iraq that showed them attacking a group of unarmed people in Baghdad in 2007. Two of them are journalists. Several were children. “Light ‘em all up,” says one of the pilots, in an incident that left a dozen dead.
Some of the material was passed to WikiLeaks by then US army intelligence analyst Chelsea Manning. Ms Manning served seven years for leaking the information, much of it in solitary confinement.
Julian Assange supporters celebrate outside court
Mr Assange spent five years in the Ecuadorian embassy in London after he sought political asylum, and as he sought to avoid extradition to Sweden where police said they wanted to investigate him over two accusations of sexual assault. Mr Assange has denied the claims and said he believed he would be taken to the US.
In April 2019, after a change in the leadership of Ecuador, Mr Assange was told he could no longer stay there and was arrested by British police and imprisoned for 12 months for skipping bail.
A month after that, the US announced it had charged him with 17 counts of trying to hack a Pentagon computer and offences under the Espionage Act, that carry penalties of 175 years in prison.
Ms Moris said it was expected that on the first day of the hearing, the US would make its case. The second day would be taken up by Mr Assange’s lawyers, who, among other things, planned to draw attention to a story published by Yahoo News that alleged that under Donald Trump, the CIA had considered plans to kidnap or murder the WikiLeaks’ founder.
Kristinn Hrafnsson, Wikileaks’ editor-in-chief, said he was not surprised by the story given the organisation had known since 2017 that then CIA Director Mike Pompeo considered the group a “non-state hostile intelligence service”.
“That was the reality on the table and we knew that we needed to be careful. This has been basically the reality for 10 or 11 years now,” he said.
“When you expose the secrets of the empire, they will come back at you.”
The charges against Mr Assange date back several years and his supporters believe Mr Trump and his government acted after WikiLeaks began in March 2017 exposing what became known as Vault 7, a series of documents that highlighted the CIA’s ability to perform electronic surveillance and carry out cyber warfare.
Supporters of Mr Assange, who argue he should receive the same protections as any other journalist or publisher, have called on President Joe Biden to halt the extradition.
Among those urging Mr Biden to act was Amnesty International’s Secretary General Agnès Callamard.
“It is a damning indictment that nearly 20 years on, virtually no one responsible for alleged US war crimes committed in the course of the Afghanistan and Iraq wars has been held accountable, let alone prosecuted, and yet a publisher who exposed such crimes is potentially facing a lifetime in jail,” she said in a statement.
The Department of Justice did immediately respond to enquiries from The Independent.
Rebecca Vincent, director of international campaigns at Reporters Without Borders, said the case this week had implications for journalists around the word.
She said: “Reporters Without Borders fully believes Julian Assange has been targeted for his contributions to journalism, and that the implications for journalism and press freedom will be severe and long lasting and not just in the US or UK, but internationally.”