WikiLeaks said it would challenge the order and that Assange’s lawyers have 14 days to file an appeal.
“We are not at the end of the road here,” said Assange’s wife, Stella Assange. “We’re going to fight this.”
Julian Assange has fought in British courts for years to avoid being deported to the US, where he faces 17 counts of espionage and one charge of computer abuse.
US prosecutors say Australian citizen helped US military intelligence analyst Chelsea Manning stole confidential diplomatic cables and military files, which were later published by WikiLeaks, putting her life at risk.
To his supporters, Assange, 50, is a breach of privacy journalist who exposed US military wrongdoing in Iraq and Afghanistan.
A British court ruled in April that Assange could be sent to face trial in the US, with the case being referred to the UK government for decision. Britain’s Home Secretary Priti Patel signed an order authorizing the extradition of Assange on Friday.
The Home Office said in a statement that the government had to approve his move to the US because “UK courts have not found that it would be oppressive, unjust or abuse of process to extradite Mr. Assange.”
Assange’s US lawyer, Barry Pollack, said it was “disappointing news that should concern anyone who cares about the First Amendment and the right to publish.”
Assange’s lawyers said they would present a new legal challenge, and legal experts say the case could take months or even years to conclude.
“If necessary, we will appeal it to the European Court of Human Rights,” said Assange’s lawyer, Jennifer Robinson.
Robinson asked the US President Joe Biden to drop the charges against Assange during Donald Trumppresided over, arguing that they presented a “grave threat” to free speech.
Assange’s supporters and lawyers say he was acting as a journalist and deserves the First Amendment’s freedom of expression. He argues that the case is politically motivated, that he will face inhumane treatment and that he will be unable to get a fair trial in the US.
Silky Carlow, director of civil liberties group Big Brother Watch, said the British government’s “participation in the political persecution of a journalist merely to reveal the uncomfortable truth to the public is appalling, wrong and shames our country.”
Lawyer Stella Assange, who married her husband in a prison ceremony in March, said Britain’s decision marked “a dark day for press freedom and British democracy”.
“Julian didn’t do anything wrong,” she said. “He has not committed any crime and is not a criminal. He is a journalist and publisher, and he is being punished for doing his job.”
Friday’s decision comes after a legal battle in Britain Supreme court,
A British district court judge initially rejected the extradition request on the grounds that the harsh US prison conditions were likely to kill Assange himself. US officials later assured that the WikiLeaks founder would not face severe treatment that his lawyers said would threaten his physical and mental health.
Those assurances prompted Britain’s High Court and Supreme Court to reverse the lower court’s decision.
Journalists’ organizations and human rights groups called on Britain to reject the extradition request. Assange’s lawyers say he could face up to 175 years in prison if convicted in the US, though US officials have said any sentence could be much less.
Amnesty International Secretary-General Agnes Callamard said on Friday that Assange’s extradition would “put him at great risk and send a cold message to journalists around the world.”
Assange is in London’s high-security Belmarsh Prison, where he was arrested in 2019 for not granting bail during a separate legal battle. Before that, she spent seven years inside the Ecuadorian embassy in London to avoid extradition to Sweden to face charges of rape and sexual assault.
Sweden dropped the sex crimes investigation in November 2019 because of the time it took, but British judges have kept Assange in prison pending the outcome of the extradition case.
Assange’s supporters say both his physical and mental health are under pressure. Stella Assange told a news conference that her husband’s condition was “deteriorating day by day.”
“I spoke to him last night as well and he was very worried. He couldn’t sleep,” she said. “But Julian is a fighter.”