Mr Assange, 49, who enraged and embarrassed Washington when his website published details of the reality of the so-called “war on terror”, faces a total of 17 charges of espionage and computer hacking in the States. He could be sentenced to as many as 175 years in a high security jail.
His fate is set to be decided by a British district judge, Vanessa Baraitser, who is due to deliver her verdict on Monday morning at London’s Central Criminal Court, better known as the Old Bailey. If the judge grants Washington’s request, a final decision will be made by Priti Patel, the home secretary, likely in consultation with Boris Johnson.
Meanwhile, lawyers for Mr Assange plan to file an appeal if they lose.
Mr Assange’s supporters point out the ruling, coming after a string of hearings that started in February of last year, is to be handed down in the Old Bailey’s Court 2, the same court room in which the Guildford Four were wrongly convicted of the Guildford pub bombings.
A number of high-profile figures in the media world who fell out with Mr Assange during the course of his work, among them former Guardian editor Alan Rusbridger, who published many scoops provided by Chelsea Manning and Mr Assange, have emerged as vocal defenders.
John Shipton, father of Julian Assange, says case against his son intended to cover up war crimes
On Sunday, WikiLeaks spokesperson Kristinn Hrafnsson told The Independent the hearing was the most important press freedom case in decades.
“What is at stake here is a basic principle about being able to report truthful information about our governments and the authorities,” he said. “And the precedent being set here if Julian Assange is extradited, is that nobody will be safe.”
Also on Sunday, Stella Morris, Ms Assange’s partner and the mother of two of his children, repeated her call for her husband to be released.
“Leading figures, from former vice presidential candidate Sarah Palin to Nobel Prize winners, such as human-rights campaigner Adolfo Perez Esquivel, have been calling for Julian’s freedom,” she wrote on the Mail on Sunday.
“So far, there has been no pardon. But tomorrow, a British magistrate will decide whether to order Julian’s extradition or throw out the US government’s request.”
She added: “Extraditing Julian would be so manifestly unjust that it seems impossible. But it is not. It is precisely at times like these when our rights are most easily taken away from us.”
Among the events exposed by WikiLeaks was an incident in 2007 in Iraq when two US AH-64 Apache helicopters targeted some buildings and then bore down on a group of people. More than a dozen were killed, including two Reuters journalists. None of them was armed.
“Oh, yeah, look at those dead bastards,” one US airman could be heard to say on the video footage.
Wikileaks published the video and a transcript in the spring of 2010. A month later, Ms Manning, then a US army intelligence analyst, was arrested, charged and convicted.
She was sentenced to 35 years by a military court, serving seven years of detention before her sentence was commuted by the outgoing Barack Obama.
Speaking from Australia last week ahead of the case, Mr Assange’s father John Shipton said he feared his son would be taken to the US and “broken in an act of revenge”.
“It’s just wretched injustice. I call it plague of malice,” he said.
Veteran journalist John Pilger, like Mr Assange an Australian citizen, said if he was extradited, then no reporters who challenged power would be safe.
He said Mr Assange was a threat to Washington because he and his organisation had “lifted America’s facade”.
“It revealed America’s routine war crimes, the lies of its policy-makers and an Orwellian surveillance,” he said.
“What’s more, the WikiLeaks revelations were 100-per-cent authentic. The public service this represents is unprecedented, it is investigative journalism at its finest.”
A total of 17 of the 18 charges against Mr Assange have been brought under the 1917 Espionage Act, which does not permit a defendant to argue they were acting in the public interest.