WikiLeaks founder Julian Assange was freed from a United Kingdom prison and was heading for a territory controlled by the United States on Tuesday, following a plea deal that appeared to have ended years of incarceration and court battles.

WikiLeaks said on the social media platform X that Assange had been granted bail in the UK, meaning he could leave London's high-security Belmarsh Prison.

He is understood to have agreed with the US Department of Justice to plead guilty to a single count of conspiracy to obtain and disseminate classified information linked to US national defense. He left Belmarsh on Monday before being bailed by the London High Court and boarding the flight. Assange is due to plead guilty on Wednesday. He is scheduled to then be sentenced to time served in the UK, and be allowed to continue his journey to his native Australia.

WikiLeaks said the deal had not been formally finalized when Assange boarded the flight and that he is expected to enter his plea on Wednesday morning in a court in Saipan, the Northern Mariana Islands, a US commonwealth in the western Pacific Ocean.

The US territory in the Pacific was chosen due to Assange's opposition to traveling to the US mainland and for its proximity to Australia, prosecutors said.

The US had pursued him for many years, contending that leaked documents published on the WikiLeaks website put its citizens in danger.

WikiLeaks has always insisted its online postings did not put people at risk, but exposed "government corruption and human rights abuses".

"After more than five years in a 2 by 3 meter cell, isolated 23 hours a day, he will soon reunite with his wife Stella Assange, and their children, who have only known their father from behind bars," the organization said.

Stella Assange told the BBC: "This is finally over."

Assange's brother, Gabriel Shipton, told Sky News his sibling was "overwhelmed to be out of prison".

Australia's Prime Minister Anthony Albanese, who is believed to have lobbied the US for Assange to be allowed to return home, said in Parliament: "Regardless of the views that people have about Assange's activities, the case has dragged on for too long. There is nothing to be gained by his continued incarceration and we want him brought home to Australia."

Agencies contributed to this story.