Olbermann returned from one last commercial break on "Countdown" to tell viewers it was his last broadcast, and read a James Thurber short story in a three-minute exit statement. Simultaneously, MSNBC e-mailed a statement that "MSNBC and Keith Olbermann have ended their contract." The network thanked him and said, "we wish him well in his future endeavors."
Olbermann was nearly fired in November, but instead was suspended two days without pay for violating an NBC News policy by donating to three political campaigns, including the congressional campaign of Arizona Rep. Gabrielle Giffords. He returned and apologized to his fans, but not the network.
MSNBC spokesman Jeremy Gaines insisted Olbermann's exit had nothing to do with the acquisition of parent company NBC Universal by Comcast, which received regulatory approval last week. That deal marked the exit of NBC Universal chief Jeff Zucker, who saw Olbermann's value in turning around a once-unprofitable network, despite headaches the mercurial personality could sometimes cause his bosses.
"There were many occasions, particularly in the last 2½ years, where all that surrounded the show - but never the show itself - was just too much for me," Olbermann said in his exit statement. "But your support and loyalty and, if I may use the word, insistence, ultimately required that I keep going. My gratitude to you is boundless."
Olbermann's father, Theodore, who was often cited when his son discussed problems in the health care system, died last March. His mother died the year before.
"A lot of people are trying to figure out if this was truly voluntary or not," said Adam Green, co-founder of BoldProgressives.org, which collected thousands of petition signatures urging Olbermann's reinstatement following last fall's suspension.
After Giffords was shot in the head on Jan. 8, Olbermann took to the air with an emotional editorial that night saying politicians and talk show personalities - including himself - need to swear off any kind of violent imagery so as not to incite anybody into acts like the Giffords shooting.
Olbermann's peripatetic career landed him at MSNBC eight years ago - his second prime-time stint on the network - with a humorous show counting down the day's top stories. That changed on Aug. 30, 2006, when Olbermann aired the first of a series of densely-worded and blistering "special comments," this time expressing anger at then-Defense Secretary Donald Rumsfeld's criticism of opponents to the war in Iraq.
More anti-Bush administration commentary followed. Olbermann dropped any pretense of journalistic objectivity, and he became a hero to liberals battered by the popularity of Fox News Channel and its conservative commentators. Olbermann openly feuded with Fox, often naming personalities like Bill O'Reilly and Glenn Beck one of his "worst persons in the world" for some of their statements.
"Countdown" became MSNBC's most popular show. Instantly, a network that had often floundered in seeking a direction molded itself after Olbermann. Opinion was in, and MSNBC's prime-time lineup was filled out with Rachel Maddow and Lawrence O'Donnell, who both had been subs for Olbermann when he was away.
Olbermann, before leaving the show with a final signature toss of his script toward the camera on Friday, thanked his audience for sticking with him. As was often his habit on Friday nights, he read a Thurber short story, this one titled "Scottie Who Knew Too Much" and published in 1940.
The story's final line: "It is better to ask some of the questions than to know all of the answers."
He thanked several people, including the late Tim Russert, but pointedly not Griffin or NBC News President Steve Capus.
He said he was grateful to the network that he was given time to sign off, noting that when he left ESPN in the 1990s, he was given 30 seconds - cut in half at the last minute to get in tennis results.
David Brock, founder and CEO of the liberal media watchdog Media Matters for America, said Olbermann "led the charge" against "conservative misinformation in prime time."
"Keith is an innovator and extremely talented broadcaster who showed there was a market for progressive views on cable news," Brock said. "I'm sure we'll be hearing more of him soon, and I eagerly await hearing of his next move."
The mood was different at Newsbusters, a website operated by the conservative Media Research Center: "You guys at Newsbusters should really break out the champagne and party," wrote one reader about Olbermann.
MSNBC announced that O'Donnell, who had frequently filled in for Olbermann before starting his own 10 p.m. show, will take over Olbermann's time slot starting Monday. "The Ed Show," with Ed Schultz, will move to 10 p.m. Cenk Uygur of the Web show "The Young Turks" will fill Schultz's vacated 6 p.m. time slot.
Olbermann's plans are unclear. He signed a four-year contract with MSNBC two years ago; contract buyouts typically include noncompete clauses that keep a personality off TV for a period of time.
CNN has continued to struggle in prime time, most recently with a program in Olbermann's time slot hosted by Eliot Spitzer and Kathleen Parker. Bringing Olbermann on, however, would mean a dramatic shift in the network's determined nonpartisan stance, and there was no indication such a change was imminent.