Julian Assange will hand himself over to police for arrest on Friday if the UN rules that he has not been unlawfully detained.
The Metropolitan Police have said they will make "every effort" to arrest Mr Assange should he leave the Ecuadorian Embassy in London where he has been for more than three years.
The WikiLeaks founder is wanted for questioning in Sweden over one allegation of sexual assault, which he has always denied, and is fighting against extradition.
He was granted political asylum by the South American nation and has remained in their embassy since breaking police bail in 2012.
He has previously claimed that if he goes to Sweden he will be handed over to US authorities who have an espionage case against him and want to question him over the activities of WikiLeaks.
However in a statement published by the activist group early on Thursday, Mr Assange said he expected to be able to walk free if the British and Swedish authorities fail to receive UN approval for extradition.
He said: "Should the UN announce tomorrow that I have lost my case against the United Kingdom and Sweden I shall exit the embassy at noon on Friday to accept arrest by British police as there is no meaningful prospect of further appeal.
"However, should I prevail and the state parties be found to have acted unlawfully, I expect the immediate return of my passport and the termination of further attempts to arrest me."
The statement was signed: "Julian Assange, Embassy of Ecuador, London."
According to the website justice4assange.com the 44-year-old Australian has so far spent 1885 days "under house arrest".
He was arrested under a European Arrest Warrant in 2010 to answer "serious criminal allegations" in Sweden and after a legal battle his extradition was granted by the Supreme Court in May 2012.
Mr Assange was subject to arrest under British law when he failed to surrender for transfer to Sweden on June 29 2012 after entering the Ecuadorian embassy.
The building in Knightsbridge, one of London's most affluent areas, is a short distance from Harrods department store and was put under round the clock supervision by Scotland Yard until October, when they removed their officers.
The building remained under covert surveillance.
A Met spokesman said: "The operation to arrest Julian Assange does however continue and should he leave the Embassy the MPS will make every effort to arrest him.
In September 2014 Mr Assange filed a complaint against Swedish and the UK authorities which has been considered by a group of legal experts for the UN who are expected to deliver their findings on Friday.
The UN Working Group on Arbitrary Detention has made previous rulings on whether imprisonment or detention is lawful, although the group does not have any direct bearing on British and Swedish authorities.
If the working group finds Mr Assange's detention to be unlawful the UN is expected to call on the UK and Sweden to let him go free.
The campaigner and former hacker has offered to be interviewed by Swedish prosecutors, while the Ecuadorian president, Rafael Correa, said their questions could also be put by Ecuadorean officials.
Marianne Ny, the Swedish prosecutor handling the case, was believed to be considering a request to allow embassy officials to question their guest.