"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," he said.
"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," he said in a statement issued by WikiLeaks on Twitter.
He took refuge in the embassy to avoid extradition to Sweden where two women have accused him of sexual assault. He denies the allegations.
In 2014, Assange complained to the UN that he was being "arbitrarily detained" as he could not leave the embassy without being arrested.
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The UK Foreign Office, on the other hand, claimed Assange had voluntarily avoided lawful detention, saying it still had an obligation to extradite him.
Wikileaks, founded by Assange in 2006, released 500,000 secret military files on the wars in Afghanistan and Iraq and 250,000 diplomatic cables enraging the United States.
He fears being extradited to the US to be quizzed over the activities of WikiLeaks if he travels to Sweden, as the main source of the leaks, US soldier Chelsea Manning, was sentenced to 35 years in prison for breaches of the Espionage Act.
Last month, it emerged that he is to be questioned by Swedish authorities over the sexual assault allegations at his Ecuadorean embassy hideout in London.
Negotiations began in June last year between Ecuador's acting foreign minister, Xavier Lasso, and the Swedish justice ministry's international affairs chief, Anna-Carin Svensson.
In September 2014, Assange filed a complaint against Sweden and Britain to the UN Working Group on Arbitrary Detention claiming his confinement in the embassy amounts to illegal detention.