The Australian whistleblower's lawyer admitted to feeling downbeat over his client's chances.
The ruling by Judge Howard Riddle at Belmarsh Magistrates Court was however unlikely to be the final word, with the losing party expected to lodge an appeal which would postpone the ultimate decision until as late as Britain's summer.
Mark Stephens, Assange's lawyer, admitted in the Independent newspaper that he was prepared for bad news.
"Both sides, the prosecution and the defence, have told the judge that they are going to appeal if they lose, so we are already working on that
principle," he said.
Assange, 39, is currently free on bail in Britain fighting against extradition for interrogation and possible trial over allegations from two Swedish women of rape and sexual molestation.
During three days of hearings held earlier in the month, Assange's legal team argued that the Swedish prosecutor had no power to issue a European arrest warrant and that the charges did not amount to extradition offences.
The campaigner's lawyers also said he would 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 US where he could face the death penalty.
Senior lawyer Julian Knowles, an expert on extradition law, said that Assange's defence was likely to fail.
"There is no doubt that a Swedish prosecutor does have the power to issue warrants," Knowles told BBC's Law in Action radio programme.
"The Swedish prosecutor has made it clear that Assange is wanted for trial if he goes back. Unless he can demonstrate his innocence before trial, he will be tried."
Knowles said it was "obvious" that the alleged offences constituted sexual assault and that to prevent extradition on the grounds of unfair trial, Assange would need to demonstrate that "there would be no meaningful trial at all."
Assange rocked the world's diplomatic institutions last year when his WikiLeaks website began releasing over 250,000 leaked cables sent by US embassy staff.
Assange claimed his greatest fear was eventual extradition to the US, where his lawyers argued he could be sent to Guantanamo Bay detention facility or face the death penalty.
"That is, frankly, a hopeless argument," Knowles said.
Amy Jeffress, the US justice department's attache to the American embassy in London, agreed with Knowles's conclusion.
"The president...has decided to close Guantanamo Bay," she told the BBC show. "No one is going to Guantanamo Bay and that claim is baseless."