But even though he may leave with the support of a United Nations working group, he is still likely to be arrested in Britain on sex crime charges for alleged crimes in Sweden that date back several years.
The U.N. working group is believed to have decided Assange is being unlawfully detained, according to the Press Association, a British news organization. The decision is scheduled to be published Friday.
Assange had said he would surrender to British police for arrest Friday if the U.N. group ruled he had not been unlawfully detained.
However, any judgment by the U.N. Working Group on Arbitrary Detention would be only a "moral recommendation" and would not be legally binding. And British police are still expected to arrest Assange if he leaves the Ecuadorian Embassy, where he has been holed up since June 2012.
CNN has not confirmed the decision by the U.N. working group. When asked Thursday, a U.N. spokesperson said: "Tomorrow morning we will release the official opinion of the working group and we cannot comment until the decision is made public tomorrow. Whatever is seen in reports today is not official."
Assange said he submitted a complaint to the U.N. Working Group on Arbitrary Detention about his case in 2014. Justice For Assange, a site set up to fight for his release, said the panel is expected to rule this week on whether Assange's detention arbitrarily deprived him of his liberty -- in other words, whether it is illegal.
"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," Assange said in a statement posted by WikiLeaks.
But, Assange added that if the panel ruled in his favor, "I expect the immediate return of my passport and the termination of further attempts to arrest me."
London police ended their 24-hour guard of the embassy in October, saying it was no longer "proportionate." But a London Metropolitan Police representative told CNN that the department's position on Assange has not changed, and he would be arrested if he left the embassy, with police considering the use of "covert tactics."
Assange, an Australian, has not been charged and has denied the rape claim. He says it is retaliation for WikiLeaks having released thousands of pages of government secrets.
He has said he fears Sweden would extradite him to the United States, where he could face the death penalty if he is charged and convicted of publishing those documents.
The Swedes, who want to question him for sex crime allegations unrelated to WikiLeaks, issued an arrest warrant in 2010. Assange was in London at the time.
As he fought to have the warrant dismissed, Ecuador granted him political asylum, and he's been living in its London embassy ever since.
'Framed by political events'
In his appeal to the U.N. Working Group on Arbitrary Detention, Assange said his confinement has deprived him of access to fresh air, sunlight and adequate medical care. He says he is subject to round-the-clock surveillance and remains in a constant state of insecurity.
"This is an application framed by political events," he wrote. "(I)t could be distilled to the simple and irrefutable fact that a political refugee, who has never been charged, has been deprived of their liberty for nearly four years, and confined in a very small space for over two years."
In other instances of detention, the U.N. working group called for the release of Aung San Suu Kyi in Myanmar after years of house arrest. The group has also ruled for the release of former Egyptian President Mohamed Morsy, but he remains in prison.