"Yesterday, in the Westminster Magistrates Court in London, the lawyers for WikiLeaks co-founder Julian Assange presented to the judge a document from me stating that I have put up $20,000 of my own money to help bail Mr. Assange out of jail," Moore said in a statement posted online.
Filmmakers Ken Loach and John Pilger and writer Jemima Kahn joined Moore in the contributing to Assange's bail fund, Moore said.
Moore also offered "the assistance of my website, my servers, my domain names and anything else I can do to keep WikiLeaks alive and thriving."
Assange appeared in a London court Tuesday, where he sought to fight his extradition to Sweden in a sex-crimes investigation and secured bail after being held for a week in a British prison cell. But while he was granted bail by a British court, he remained in police custody as Swedish authorities challenged the decision.
The move will keep Assange in jail for another 48 hours, Fox News learned.
But several celebrities, including Jemima Khan and Hanif Kureishi pledged their support to Assange, despite international outcry.
Moore addressed the rape charges filed against Assange.
"For those of you who think it's wrong to support Julian Assange because of the sexual assault allegations he's being held for, all I ask is that you not be naive about how the government works when it decides to go after its prey. Please -- never, ever believe the 'official story,'" Moore said in the statement.
The 39-year-old Australian was ordered held in custody by a judge at a hearing a week ago after surrendering himself to Scotland Yard to answer a Swedish arrest warrant.
Assange remained defiant in comments from prison relayed Tuesday by his mother.
"My convictions are unfaltering," the network quoted Julian Assange as saying. "I remain true to the ideals I have expressed. This circumstance shall not shake them. If anything, this process has increased my determination that they are true and correct."
Assange is wanted for questioning after two women accused him of sexual misconduct in separate encounters in Sweden over the summer. Lawyers for Assange say he denies the allegations and will contest the attempt to extradite him for questioning.
Assange's lawyer, Mark Stephens, said his client would offer to be electronically tagged and stay at an address known to the police.
"One's never going to count one's chickens until they're hatched, but I hope that in these circumstances the district judge will feel confident" granting bail, Stephens told Sky News.