Julian Assange will formally begin his fight against being handed over to the US, where he faces accusations he helped leak hundreds of thousands of classified documents.
The WikiLeaks founder is due to appear in a London court on Monday for the first day of his full extradition hearing.
The 48-year-old is wanted in America on 18 charges over the publication of US cables a decade ago and if found guilty could face a 175-year prison sentence.
The Australian is accused of working with former US army intelligence analyst Chelsea Manning to leak classified documents.
In the lead-up to the hearing, Assange, who is being held in Belmarsh Prison in south-east London, has received high-profile support including from Pink Floyd’s Roger Waters, Greek economist Yanis Varoufakis and fashion designer Vivienne Westwood.
He has also been supported at previous court timetabling hearings by Rapper M.I.A. and filmmaker John Pilger.
A day before his appearance at the nearby Woolwich Crown Court, Assange’s father John Shipton claimed his son had been “harassed” by a prison cell search.
After a visit to the prison on Sunday, Mr Shipton criticised the “plague of malice” which he said “emanates from the Crown Prosecution Service” towards Assange.
He urged that his son be allowed bail, telling reporters: “For the life of me I can’t understand why Julian Assange is in jail having committed no crime, with family here that he can come and live with.”
Mr Varoufakis said Assange was in a “very dark place” due to spending more than 20 hours a day in solitary confinement and called for the extradition to be stopped “in the interests of 300 years of modernity, 300 years of trying to establish human rights and civil liberties in the west and around the world”.
More than 40 international legal experts have written to Prime Minister Boris Johnson demanding the “rule of law be upheld”, claiming he has not had proper access to his legal team.
The letter was handed in to 10 Downing Street on Saturday and also urged the British legal community to act “urgently” to secure Assange’s release.
Assange has been held on remand in Belmarsh prison since last September after serving a 50-week jail sentence for breaching his bail conditions while he was in the Ecuadorian embassy in London.