The founder of whistle-blowing website Wikileaks, Julian Assange, has vowed "to continue my work and to protest my innocence" after being freed on bail.
The 39-year-old was granted bail two days ago but prosecutors objected.
He is fighting extradition to Sweden over sex assault allegations made by two women. He denies any wrongdoing.
Mr Justice Ouseley ordered Mr Assange be released on payment of £240,000 in cash and sureties and on condition he resides at an address in East Anglia.
Speaking on the steps of the High Court to dozens of journalists, Mr Assange said: "It's great to feel the fresh air of London again."
He went on to thank "all the people around the world who had faith" in him, his lawyers for putting up a "brave and ultimately successful fight", people who provided money in the face of "great difficulty and aversion", members of the press and the British justice system.
"If justice is not always an outcome, at least it is not dead yet," he added.
"I hope to continue my work and continue to protest my innocence in this matter and to reveal as we get it, which we have not yet, the evidence from these allegations."
Mr Assange had spent the past eight nights in prison.
He will now stay at a manor home on the Norfolk-Suffolk border owned by Vaughan Smith, a Wikileaks-supporting journalist and owner of the Frontline Club in London.
Mr Assange's solicitor, Mark Stephens, said after the court appearance the bail appeal was part of a "continuing vendetta by the Swedes".
At the SceneAs the rain turned to snow outside the Royal Courts of Justice, Julian Assange finally appeared before the world's media.
Wearing a dark suit and opened-necked shirt, he was lit up by scores of camera flashes capturing his first moments of freedom.
Behind the rows of journalists, photographers and camera crews supporters of Mr Assange chanted, "Julian, Julian, Julian, out, out out!" clearly delighted with the news.
It had appeared touch and go whether he would be released on Thursday, with rumours circulating as to how late the court would be prepared to stay open in order to finalise the paperwork for his freedom.
Not everyone at the court was interested in the Wikileaks founder though. One woman spent the entire day parading around a placard complaining about a parking fine she had received in north London.
But the question of who decided to appeal against the granting of bail remains unclear.
A CPS spokesman said on Thursday: "The Crown Prosecution Service acts as agent for the Swedish government in the Assange case. The Swedish Director of Prosecutions this morning confirmed that she fully supported the appeal."
But earlier Nils Rekke, from the Swedish Prosecutor's Office, claimed it was "a purely British decision".
Speaking to the BBC after his release, he said there was a rumour from his lawyers in the US that there had been an indictment made against him there.
A spokeswoman from the US Department of Justice would only confirm there was "an ongoing investigation into the WikiLeaks matter".
Mr Assange's mother, Christine, said she was "very, very happy" with the decision and thanked his supporters.
"I can't wait to see my son and to hold him close. I had faith that the British justice system would do the right thing and the judge would uphold the magistrates' decision, and that faith has been reaffirmed," she said.
Gemma Lindfield, representing the prosecution, had told the judge there was "a real risk" Mr Assange would abscond, and pointed to his nomadic lifestyle.
She said he had "the means and ability" to go into hiding among Wikileaks' many supporters in this country and abroad.
But Mr Justice Ouseley pointed out Mr Assange, who is Australian, had offered to meet the police in London when he heard the Swedish matter was still live and he said: "That is not the conduct of a person who is seeking to evade justice."
However, he did impose strict bail conditions including wearing an electronic tag, reporting to police every day, observing a curfew and residing at Mr Smith's home.
Earlier, the judge made a ruling banning the use of Twitter to give a blow-by-blow account of Thursday's proceedings.
Mr Assange has received the backing of a number of high-profile supporters, including human rights campaigners Jemima Khan and Bianca Jagger, and film director Ken Loach.
Wikileaks has published hundreds of sensitive American diplomatic cables, details of which have appeared in the Guardian in the UK and several other newspapers around the world.
He has been criticised in the US, where former Republican vice-presidential candidate Sarah Palin has said he should be hunted down like the al-Qaeda leadership.
Mr Assange argues the allegations against him are politically motivated and designed to take attention away from the material appearing on Wikileaks.
Bail sureties providers
- Phillip Knightley - Australian journalist
- Felix Dennis - publisher
- Sir John Sulston - Nobel-winning scientist
- Lord Matthew Evans - Labour peer
- Prof Patricia David
Speaking to the BBC, he said Wikileaks would continue its work.
"We have seen in my week away that my team is robust, support for them is strong and we were fortunately able to continue publishing, in a very efficiently successful manner, even though I was taken out briefly," he said.
"That does not underestimate the risks faced by all of us, but it does show the resilience of the organisation, that it can withstand decapitation attacks."
Mr Assange is accused of having unprotected sex with a woman, identified only as Miss A, when she insisted he use a condom.
He is also accused of having unprotected sex with another woman, Miss W, while she was asleep.
A full extradition hearing should normally take place within 21 days of the arrest. Mr Assange was arrested on 7 December, so this should be by 28 December.
However, in such a high profile case, it is possible that a full extradition hearing will not take place for several months.
At that hearing Mr Assange will be able to challenge the warrant and raise any defences to the extradition request.