Julian Assange will marry his long-term partner Stella Moris in a small ceremony inside a high-security London prison while his supporters will gather to celebrate outside.
The ceremony will take place in Belmarsh prison, just weeks before the third anniversary of the WikiLeaks founder's dramatic arrest when he was dragged out of the Ecuadorian embassy.
The wedding is expected to be attended by four guests, two official witnesses and two security guards.
Assange has been held in the high-security jail as he fights extradition to the United States, where he is wanted over an alleged conspiracy to obtain and disclose national defence information.
That follows WikiLeaks' publication of hundreds of thousands of leaked documents relating to the Afghanistan and Iraq wars.
The 50-year-old, who denies any wrongdoing, has been held at Belmarsh prison since 2019 and before that was holed up in the Ecuadorean embassy in London for seven years. He has won support for his case from human rights organisations and journalist groups across the world.
While living at the embassy he fathered two children with Ms Moris, a lawyer more than a decade his junior, who he met in 2011 when she started work on his legal team. Their relationship began in 2015.
The registrar-led ceremony will take place during visiting hours at the prison, where some of Britain's most notorious criminals have served sentences, including child murderer Ian Huntley.
Ms Moris' wedding dress and Assange's kilt - a nod to his family ties to Scotland - have been created by British fashion designer Vivienne Westwood, who has previously campaigned against his extradition.
His fiancée has spoken of her joy at being allowed to marry the WikiLeaks founder despite restrictions being placed on their wedding.
The guests will have to leave immediately after the event.
Ms Moris said: "Obviously we are very excited, even though the circumstances are very restrictive.
"All the guests and witnesses must leave as soon as the ceremony is over, even though that will be before normal visiting time ends.
"Julian is looking forward to the wedding because it is finally happening, many months after we first made the request."
A Prison Service spokesperson said: "All weddings in prisons must meet the requirements outlined in the Prison Service policy."
The service said photography for weddings in prisons is facilitated by prison staff, in line with "established national policy on photographing prisoners".
It added: "The relevant policy makes clear the governor can block images being taken if it is believed they will be shared publicly, which can compromise prison security. Accordingly, photos will be taken by prison staff."
The cost of the ceremony will be picked up by the couple.
Supporters have been asked to dress as if they were attending a wedding.
Instead of sending gifts, it was suggested they donate to the new official Crowdfunder campaign, sponsor a park bench or similar in their area, and put up posters calling for Assange to be freed.
Assange was denied permission this month to appeal at the Supreme Court against a decision to extradite him to the United States. He could still challenge any decision from the government to approve his extradition.
