The high court upheld a ruling in February by District Judge Howard Riddle at Belmarsh Magistrates’ Court, south London, that Mr Assange should be extradited to face investigation.
Judges ruled Mr Assange should face sexual assault charges in Sweden, where he is wanted to answer allegations he “raped” one woman and “sexually molested and coerced” another in Stockholm in August last year.
Mr Assange‘s lawyers had asked two judges to rule that extraditing the 40-year-old Australian would be “unfair and unlawful”.
Judgement was handed down by President of the Queen’s Bench Division, Sir John Thomas, sitting with Mr Justice Ouseley.
The Assange legal challenge, which has attracted worldwide attention, centred on a European arrest warrant (EAW) issued by a Swedish prosecutor which led to Assange’s arrest.
Assange, whose WikiLeaks website published a mass of leaked diplomatic cables that embarrassed several governments and international businesses, denies the allegations and says they are politically motivated.
The famous whistle-blowing site founded by Mr Assange faces having to stop publishing secret cables and devote itself instead to fund-raising because of a financial block on payments to the site by US firms such as Visa and MasterCard.
Mr Assange said if the block was not ended by the turn of the year, WikiLeaks would not be able to continue.
Statement by Julian Assange Speaking outside the high court in London after it had upheld the extradition ruling, Mr Assange said: "The European arrest warrant is so restrictive that is prevents UK courts from considering the facts of a case." He continued: "The full judgement will be available on swedenversusassange.com. "No doubt there will be many attempts made to try to spin these proceedings as they occurred today, but they are merely technical."