Omidyar, the 46-year-old French-born Iranian-American who remains chairman of the e-commerce giant he founded, wrote in a blog post that he considered buying the Washington Post - which Amazon.com Inc founder Jeff Bezos eventually snapped up - but decided he wanted to build a news organization from the ground up.
"Right now, I'm in the very early stages of creating a new mass media organization. I don't yet know how or when it will be rolled out, or what it will look like," he wrote.
"I developed an interest in supporting independent journalists in a way that leverages their work to the greatest extent possible, all in support of the public interest. And, I want to find ways to convert mainstream readers into engaged citizens. I think there's more that can be done in this space, and I'm eager to explore the possibilities."
Omidyar's active Twitter feed suggests he is very concerned about government-spying programs exposed by Greenwald and former U.S. government contractor Edward Snowden. In his blog post, Omidyar spoke of his growing interest in the role that journalism plays in society, and his own support of efforts to promote government accountability and transparency.
Omidyar, who is no longer involved in day-to-day operations at eBay, stressed that his venture would remain separate from his numerous philanthropic, business and political interests, run mainly through an entity called the Omidyar Network.
Forbes pegged Omidyar's net worth at $8.5 billion. Among his ventures is Honolulu Civil Beat, a news website covering public affairs in Hawaii. Civil Beat aims to create a new online journalism model with paid subscriptions and respectful comment threads, though it is unclear how successful it has been.
Omidyar also founded the Democracy Fund to support "social entrepreneurs working to ensure that our political system is responsive to the public," according to its website.
Omidyar added that Greenwald's former colleagues, Laura Poitras and Jeremy Scahill, would also join his media project.
"I'll be sure to update you along the way as the new organization progresses," he said.