The case will now go to Britain’s interior minister for a decision, though the WikiLeaks founder still has legal avenues of appeal.
Assange and his fiancee will marry at Belmarsh prison in southeast London where he is on remand and fighting extradition attempts.
WikiLeaks founder had urged the British Supreme Court to allow him to appeal High Court ruling to extradite him to the United States, where he is facing a trial on 18 criminal charges including breaking a spying law.
The court ruled that United States had given a package of assurances to Britain about the conditions of Assange's detention.
A London judge ruled in January that the Wikileaks foudner should not be extradited to the United States to face criminal charges including breaking a spying law, saying his mental health problems meant he would be at risk of suicide.
Assange’s brother, Gabriel Shipton, says extradition of the Wikileaks founder to the US would be a death sentence for him and press freedom worldwide.
Assange has been detained at London’s high-security Belmarsh Prison since April 2019, when he was arrested for skipping bail during a separate legal battle seven years earlier.
The Australian Wikileaks founder shocked the world by disclosing diplomatic cables containing sensitive information.
Mexico's President Andres Manuel Lopez Obrador welcomed the British court's rejection of the US request to extradite the 49-year-old Australian due to the risk of suicide, calling it a "triumph of justice."
District Judge Vanessa Baraitser says Julian Assange likely to commit suicide if sent to the US.
If he loses the ruling, Julian Assange is likely to appeal to London’s High Court and the case could go the UK Supreme Court, further delaying the final outcome.
"Mr. Assange is not a criminal convict and poses no threat to anyone, so his prolonged solitary confinement in a high-security prison is neither necessary nor proportionate and clearly lacks any legal basis."
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