Olbermann will start this spring with a New York-based prime-time talk show on Current. He was also named chief news officer at Current, which is available in 60 million homes in the U.S., a little more than half the nation's homes with television, but has few viewers.
Financial terms were not divulged, although Current said Olbermann will get an equity stake in the company.
Olbermann's hiring was the biggest moment in the history of Current, which began as a network geared primarily toward young people featuring viewer-generated short videos and is now evolving into a more traditional network. Its showcase is the investigative documentary series "Vanguard."
"We now live in a world with fewer and fewer opportunities to hear truly unique, truly unfettered voices on television," Gore said. "Keith is one of those rare voices."
Olbermann's sudden departure from MSNBC, announced simultaneously by himself and the network on a Friday night, was never really explained. He'd been an occasional headache for his bosses, and was briefly suspended last year for making campaign contributions in violation of NBC News policy.
Yet his nightly "Countdown" show was MSNBC's most popular, and the network built a left-leaning prime-time schedule from Olbermann's template and with his proteges. Conservatives sputter at the mention of his name, but he's a hero to liberals.
"Nothing is more vital to America than a free media," Olbermann said, "and nothing is more vital to my concept of a free media than news that is produced independent of corporate interference."
Olbermann, whose MSNBC show took on an entirely new persona when he began delivering blistering commentaries on President George W. Bush's administration, said "none of this should be considered directed toward any of my nine full-time previous employers."
His new show doesn't have a name or a time slot yet, nor is it clear how Current will fill out the rest of its prime-time lineup around him.
"I'm always trying to do more or a better version of what I've done previously," he said. "I wanted my career and my involvement in news to move forward."
Olbermann, 52, began hosting "Countdown" in 2003.
He said he never considered a move back to sports, where his work on ESPN's "Sportscenter" in the 1990s pushed him to national prominence.
His way to more mainstream news networks was blocked. Olbermann has made Fox News Channel a frequent target for criticism and ridicule. Ken Jautz, chief executive of CNN's U.S. network, said this week that CNN had no interest in Olbermann.
MSNBC, which presumably has keen interest in another network trying to become known for its liberal leanings, would have no comment on Olbermann's move, spokesman Jeremy Gaines said.
Current said that as chief news officer, Olbermann would "provide editorial guidance for all of our political news, commentary and current events programming." That's a switch for a network that has always stressed its independence from the politics of a former Democratic vice president.
At his new network, Olbermann won't be barred from making political donations, as long as he publicly discloses them, Gore said.
AP Television Writer Frazier Moore contributed to this report.
Current TV is owned by Current Media.