“I must order that Mr Assange be extradited to Sweden,” judge Howard Riddle said in a decision at Belmarsh Magistrates Court in southeast London, following an extradition hearing earlier this month.
Lawyers for the 39-year-old Australian, who was detained in Britain on a Swedish arrest warrant in December, said following the ruling they planned to file an appeal.
“We will be appealing,” his main lawyer Geoffrey Robertson told the court following the ruling.
In handing down his ruling, Judge Riddle told onlookers that the crimes Assange is alleged to have committed meet the criteria for extradition, according to Twitter feeds from numerous journalists inside the courtroom.
In rejecting much of the defence team’s claims, the judge also accused Assange’s Swedish lawyer, Björn Hurtig of being unreliable.
Judge Riddle also said he doubted that comments made by Swedish Prime Minister Fredrik Reinfeldt would compromise Assange’s ability to receive a fair trial in Sweden.
Speaking after the hearing Assange criticised the European system under which he was detained in December at Sweden’s request.
“It is a result of the European Arrest Warrant system run amok. There was no consideration during this entire process as to the merits of the allegations against me,” he told around 100 journalists from across the globe.
Assange has seven days to lodge a formal appeal. The judge gave him bail on the same conditions as before, namely that he should reside at a friend’s mansion in eastern England, wear an electronic ankle tag and observe a curfew.
Celebrity backers including socialite Jemima Khan and rights campaigner Bianca Jagger were also at the court along with around 100 journalists from around the world.
Former computer hacker Assange says the claims against him, made by two women he met during a seminar organised by the whistleblowing website in August last year, are politically motivated because of the work of WikiLeaks.
Assange rocked the world’s diplomatic institutions and infuriated Washington last year when WikiLeaks began releasing more than 250,000 secret diplomatic cables sent by US embassy staff.
It has also published sensitive data on the wars in Iraq and Afghanistan.
Judge Riddle threw out arguments by Assange’s legal team that the Swedish prosecutor had no power to issue a European arrest warrant and that the allegations did not amount to extradition offences.
“In this country that would amount to rape,” Riddle said about the allegation by one woman that Assange had unprotected sex with her while she was asleep.
He said that Assange’s Swedish lawyer Björn Hurtig made a “deliberate attempt to mislead the court” when he said that he had been unable to contact Assange to arrange an interview with Swedish prosecutors.
Riddle also dismissed arguments that Assange could not face a fair trial as some evidence would be held behind closed doors, and that it was possible he would be re-extradited to the United States where he could face the death penalty.
Riddle said that the arrest warrant was valid and said he had to uphold the “mutual respect and confidence this court has in our European counterparts.”
The judge also said it was “highly unlikely” that comments by Swedish Prime Minister Fredrik Reinfeldt that Assange lacked respect for women’s rights would have an effect on the case.
Karin Rosander, a spokeswoman for the Swedish prosecutor, said only that they would “see if they appeal or not” before issuing a “very short statement” later.
His lawyer Mark Stephens criticised the “tick-box justice” of the warrant system, but added: “We still remain very optimistic about our opportunities on appeal.”
Claes Borgström, the lawyer for the two Swedish women at the centre of the claims, said it was “regrettable” that Assange was appealing but that he hoped the case would be over by summer.
“Assange must respect the principles that he has expressed about WikiLeaks and take responsibility,” he told the Swedish news agency TT.
Assange was arrested in Britain on December 7 on an international warrant issued by a Swedish prosecutor who wanted to question him over four separate allegations of sexual assault made by the two women.
He spent nine days in prison until he was released on bail in December and has since been staying at a friend’s country mansion in eastern England under strict conditions including that he obey a curfew, wear an electronic ankle tag and report to police daily.
The judge relaxed his conditions for Thursday’s hearing to allow him to spend the previous night at the Frontline media club in London.
Assange claimed his greatest fear was eventual extradition to the United States, where his lawyers argued he could be sent to the Guantanamo Bay detention facility or face the death penalty.
He recently said his site was “significantly influential” in the fall of Tunisian leader Zine El Abidine Ben Ali, an event he said “no doubt” sparked uprisings across the Middle East.
The United States said the case was solely a matter for Britain and Sweden.
“Notwithstanding claims to the contrary, the US is not involved,” State Department spokesman Philip Crowley said in a Twitter message.
Assange has claimed his greatest fear was eventual extradition to the United States, where his lawyers argued he could be sent to the Guantanamo Bay detention facility or face the death penalty.
WikiLeaks last November began publishing around 250,000 US diplomatic cables. It has also leaked thousands of secret documents about the wars in Afghanistan and Iraq.