Assange, who is fighting extradition to Sweden for questioning on sex crimes allegations, emerged from London's neo-Gothic High Court to address supports before driving off to the 10-bedroom home where he is due to spend much of the next month.
"It's great to smell the fresh air of London again," Assange told cheering supporters amid a barrage of flash bulbs.
A Wikileaks spokesman said Assange would be able to make use of the mansion's fast internet connection and return to work.
Assange gave no indication of what his immediate plans were, but said the period he spent in prison had given him time to reflect on the condition of inmates elsewhere. He didn't respond to shouted questions from assembled journalists, returning inside the court to get into his lawyer's car.
Assange is headed to Ellingham Hall, in Bungay, which is owned by Vaughan Smith, a WikiLeaks supporter and founder of London's Frontline Club for journalists. Assange will have to observe a curfew, wear an electronic tag and report to police every day - restrictions imposed by High Court Justice Duncan Ouseley.
Assange denies sex-crimes allegations stemming from a visit to Sweden over the summer, accusations that have clouded his reputation and prompted complaints from supporters that the 39-year-old Australian is being persecuted for political reasons.
Two women have accused Assange of rape, molestation and unlawful coercion in separate incidents in August in Sweden. He has not been charged.
Assange's lawyers say the allegations stem from a dispute over "consensual but unprotected sex" and argue that he has offered to make himself available for questioning via video link or in person in Britain.
Lawyer Gemma Lindfield, acting for Sweden, said the allegations had enhanced Assange's reputation among his supporters, who "view it as part of the wider conspiracy." She said given Assange's nomadic lifestyle and loose ties to some of those promising bond, there was "a real risk" he would flee.
But the judge said when Assange arrived in Britain, he had asked his lawyers to contact police so they would know where he was.
"That is not the conduct of a person who is seeking to evade justice," Ouseley said.
Swedish Prosecutor Marianne Ny said the bail decision would not change the ongoing investigation in Sweden, and the extradition case would be handled by British authorities.
Assange's next extradition hearing is set for Jan. 11.