The Wikileaks founder, Mr Julian Assange, was arrested in London on Tuesday at the height of an international outcry over the continued publication of confidential US diplomatic cables by his organisation.
Scotland Yard said the 39-year-old Australian was detained on a European arrest warrant, issued by Sweden, in connection with sexual assault claims made against him there.
Mr Assange was detained after he presented himself at a London police station "by agreement" early on Tuesday, the Scotland Yard said.
"Officers from the Metropolitan Police Extradition Unit have on Tuesday morning arrested Mr Julian Assange on behalf of the Swedish authorities on suspicion of rape," a police statement said.
His lawyers said earlier that Mr Assange had agreed to speak with Scotland Yard officers following the receipt of a European Union arrest warrant on Monday.
Mr Assange is due to appear in court in London later on Tuesday.
Mr Assange's Wikileaks organisation has sparked daily headlines around the world with its leak of top secret US diplomatic cables, and previous leaks of US Pentagon papers on the Iraq and Afghan conflicts.
Mr Assange's lawyer, Mr Mark Stephens, earlier described the arrest warrant against his client as a "political stunt" which could lead to him being handed over to the US authorities.
"It's about time we got to the end of the day and we got some truth, justice and rule of law," Stephens told the BBC late on Monday.
"Mr Julian Assange has been the one in hot pursuit to vindicate himself to clear his good name," he added.