Assange is due to be sentenced to 62 months of time already served at a hearing in the Northern Mariana Islands, a territory of the United States in the western Pacific.

He is expected to return home after that hearing, on the island of Saipan.

WikiLeaks posted a statement on social media saying Mr Assange was free and left the UK on Monday morning local time.

Part of the statement read: "This is the result of a global campaign that spanned grassroots organisers, press freedom campaigners, legislators and leaders from across the political spectrum, all the way to the United Nations.

"This created the space for a long period of negotiations with the US Department of Justice, leading to a deal that has not yet been formally finalised."

The Australian government has long been pushing the US to resolve the case, which has for years been tied up in British courts.

In May, the UK's highest court allowed him to lodge another appeal against his extradition to the US, which was due to be heard in July.

Family grateful ordeal is coming to an end

Mr Assange's parents have expressed joy and relief over their son's release.

"I am grateful that my son's ordeal is finally coming to an end," Christine Assange said.

"This shows the importance and power of quiet diplomacy.

"Many have used my son's situation to push their own agendas, so I am grateful to those unseen, hard-working people who put Julian's welfare first.

"The past 14 years have obviously taken a toll on me as a mother, so I wish to thank you in advance for respecting my privacy."

Mr Assange's father, John Shipton said his son had spent 15 of his most productive years "in some form of incarceration or another".

"The appearances are that Julian will be able to enjoy ordinary life with his family and his wife, Stella, that's my understanding," he said of the plea deal.

"It looks as though Julian will be free to come back to Australia and my thanks and congratulations to all his supporters in Australia that have made that possible, and of course Prime Minister Anthony Albanese."

In a video message recorded (above #2) on Wednesday June 19, Stella Assange said she was confident this period of their lives had come to an end.

"By this time next week, I'm confident he will be free," she said.

"Things are moving very quickly and it is very difficult for us to plan or even play out the next few hours and days.

"If everything goes well, Julian will be on a plane on the way to freedom."

She added: "We still need your help, what starts now with Julian's freedom is a new chapter.

"This new chapter in Julian and our lives, we ask for your support. In the coming hours we intend to start an emergency fund for Julian's health and recovery."

WikiLeaks editor-in-chief Kristinn Hrafnsson also prerecorded a message.

"I can say in earnest that without your support this would have never materialised — this important day of joy, the day of Julian's freedom," he said.

"Thank you so much."

Legal document outlines single criminal charge:

An Australian government spokesperson said it was too early to comment on Mr Assange's release, given legal proceedings were ongoing.

"The Australian government continues to provide consular assistance to Mr Assange," the spokesperson said.

"Prime Minister Albanese has been clear — Mr Assange's case has dragged on for too long and there is nothing to be gained by his continued incarceration."

The Australian government has been pushing the US to resolve the case and allow Mr Assange to return home.

In February, the Lower House passed a motion — supported by Labor, the Greens, independents and Liberal MP Bridget Archer — urging the US and the UK to drop the case and allow Assange's return to Australia.

And last year, a delegation of MPs from the Labor, Liberal, National and Greens parties and independent Monique Ryan travelled to Washington to lobby members of Congress.

The US Justice Department has long refused to publicly discuss the case. But in April, President Joe Biden said "we're considering it" when asked if he had a response to Australia's request that he end Mr Assange's prosecution.

Filings in the US District Court for the Northern Mariana Islands show that US prosecutors have filed criminal paperwork against Mr Assange that is typically a preliminary step before a plea deal.

The paperwork outlines a single criminal count of conspiring to obtain and disclose classified US national defence documents.

Sources | ABC / Wires