KEITH OLBERMANN OUT AT MSNBC…. Usually a move like this is preceded by some kind of scuttlebutt, but the announcement at the end of last night’s “Countdown” was one few saw coming.

Keith Olbermann, the highest-rated host on MSNBC, announced abruptly on the air Friday night that he was leaving his show, “Countdown,” immediately.

The host, who has had a stormy relationship with the management of the network for some time, especially since he was suspended for two days last November, came to an agreement with NBC’s corporate management late this week to settle his contract and step down. […]

In a statement, MSNBC said: “MSNBC and Keith Olbermann have ended their contract. The last broadcast of ‘Countdown with Keith Olbermann’ will be this evening. MSNBC thanks Keith for his integral role in MSNBC’s success and we wish him well in his future endeavors.”

The news was so sudden, MSNBC was still airing Olbermann promos last night after he’d announced his departure from the network.

Olbermann had signed a four-year contract extension in 2008 — worth an estimated $30 million — that would have kept him at MSNBC through the 2012 presidential election. With his departure, Olbermann will instead be off television for a while — the agreement reached with the network stipulates that the host will not move to a rival network for an extended period of time.

The obvious question — why in the world MSNBC would part ways with its highest-rated host — remains something of a mystery. It’s only been 11 hours since Olbermann made the announcement, so presumably we’ll learn more in the near future, but in the interim, there’s ample speculation about the effects of Comcast’s impending takeover of NBC Universal, though the network insisted last night that the development is unrelated.

It seems fairly clear, though, that the shake-up was not the host’s decision. Olbermann began the segment telling viewers, “I think the same fantasy popped into the head of everybody in my business who has ever been told what I have been told: this will be the last edition of your show….”

Lawrence O’Donnell’s “The Last Word” will now move to 8 p.m. eastern, with Ed Schultz moving to 10 p.m. eastern. Rachel Maddow’s show will stay right where it is.

As the dust settles, it’s worth emphasizing just how important Olbermann has been in American media in recent years. When he returned to prime time after a four-year absence, Olbermann offered news consumers something we couldn’t find anywhere else: honest, sincere, unapologetic liberalism. Olbermann helped shine a light on important stories that were ignored by other shows and other networks, helped give a voice to a perspective that was discounted throughout the mainstream media, picked fights with those who too often went unchallenged, and featured guests who were frequently and needlessly left out of the larger broadcast conversation.

Olbermann did all of this, of course, while racking up big ratings (and big profits for his employer), proving that there’s an audience for on-air commentary and analysis from the left, and clearing the way for others to do the same.

In the time Olbermann is off the air, he will be sorely missed.

If you missed his signoff, here it is:

Visit for breaking news, world news, and news about the economy

Our ideas can save democracy... But we need your help! Donate Now!

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.