Julian Assange has lodged an appeal against a decision by the UK government to extradite him to the United States.
Home Secretary Priti Patel approved the extradition to the US last month, but an appeal application was submitted to the High Court on Friday.
Supporters staged protests ahead of his 51st birthday on Saturday.
His wife Stella was among people who gathered outside the Home Office in central London on Friday to step up calls for the WikiLeaks founder to be released from prison.
He will spend his birthday in Belmarsh Prison in London while a lengthy legal battle continues over whether he can be extradited.
The Australian has been at the centre of a protracted legal fight for more than a decade.
Julian Assange through the years - in pictures
Mr Assange is wanted by American authorities over documents leaked in 2010 and 2011 related to the Iraq and Afghanistan wars.
He has been in prison since he was dragged out of the Ecuadorian embassy in London in 2019, where he had been living since 2012.
When the Home Office announced the extradition decision in June, his wife pledged to fight the decision with “every available avenue”, saying: “I’m going to use every waking hour fighting for Julian until he is free.”
She said her husband had told her “recently” that he planned to kill himself if he was extradited.