Assange faces espionage charges in the U.S. in 18 criminal cases for endangering lives by publishing hundreds of thousands of classified military documents and diplomatic cables between 2010 - 2011.

Assange had retained the standard 14-day right to appeal. The case passed to the home secretary in May after the U.K. Supreme Court gave a clean chit to U.S.'s assurances over Assange's fair treatment, the Guardian reports.

WikiLeaks looked to appeal the decision, calling it a "dark day for Press freedom and British democracy."

Assange's supporters hailed him an anti-establishment hero whose prosecution was politically motivated because he exposed U.S. wrongdoing in conflicts in Afghanistan and Iraq, CNBC reports.

Assange lost multiple appeal cases in the U.K. courts defending him based on political motivation, freedom of speech, and uncertainty over a fair trial in the U.S.

Assange's lawyers have previously claimed a possible penalty of up to 175 years in prison if convicted in the U.S. However, the U.S. government said the sentence would likely be four to six years.

Australian-born Assange spent much of the last decade in custody, either in prison or the Ecuadorian embassy in London. He is currently at high-security Belmarsh prison in London. 

Sexual assault allegations in Sweden prompted him to seek political asylum in 2012. He left the embassy in 2019 before his arrest in the U.K. for skipping bail and ultimately jailed.

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