Assange, 52, has been fighting extradition to the US, where he was facing espionage charges for obtaining and publishing classified information.
But on Tuesday Australia time, he agreed to plead guilty as part of a deal with US prosecutors which has ended his imprisonment in the UK, paving the way to return to Australia.
Soon after, Wikileaks announced he had left the UK and released a video of his journey to Stansted Airport outside of London.
Assange's wife Stella was elated.
Julian is free!!!!— Stella Assange #FreeAssangeNOW (@Stella_Assange) Words cannot express our immense gratitude to YOU- yes YOU, who have all mobilised for years and years to make this come true. THANK YOU. tHANK YOU. THANK YOU.Follow @WikiLeaks for more info soon…pic.twitter.com/gW4UWCKP44June 25, 2024
"After more than five years in a 2x3 metre 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," Wikileaks posted on X.
"WikiLeaks published groundbreaking stories of government corruption and human rights abuses, holding the powerful accountable for their actions.
"As editor-in-chief, Julian paid severely for these principles, and for the people's right to know.
"As he returns to Australia, we thank all who stood by us, fought for us, and remained utterly committed in the fight for his freedom.
Australia has long called for the US to end its pursuit, with Prime Minister Anthony Albanese directly raising the issue with President Joe Biden.
Reacting to the news on social media site X, Nationals Senator Matt Canavan wrote, "Julian Assange will finally be a free man!"
"It has taken far too long, but congrats to the many that have fought for so long for justice to prevail.
"Hopefully Julian can be reunited with his family soon."
Opposition foreign affairs spokesman Simon Birmingham welcomed the decision.
"We have consistently said that the US and UK justice systems should be respected," he said in a statement.
"We welcome the fact that Mr Assange's decision to plead guilty will bring this long running saga to an end."
Under the US deal, Assange agreed to plead guilty to a single criminal count of conspiring to obtain and disclose classified US national defence documents, according to filings in the US District Court for the Northern Mariana Islands.
Wikileaks says Assange has paid a heavy price for upholding the people's right to know. (James Ross/AAP PHOTOS)
He is due to be sentenced at a hearing on the island of Saipan at 9am local time on Wednesday.
It's unclear exactly where Assange will be by the time of that hearing.
In April at the White House, Mr Biden told reporters he was considering Australia's request to drop the charges against Assange.
Prosecutors wanted to put Assange on trial for publishing military documents about the war in Afghanistan and Iraq, which authorities said had damaged national security and endangered the lives of US agents.
Assange was arrested in the UK in 2010 on a separate matter and took refuge in Ecuador's embassy in London. He was taken from the embassy and sent to Belmarsh prison in 2019.
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