Keith Olbermann -- Fired By MSNBC

Keith Olbermann was fired by MSNBC sources tell TMZ, and we're told it had everything to do with Comcast's acquisition of NBC.

Sources connected with the network tell us ... Comcast honchos did not like Keith's defiance and the way he played in the sandbox.

Our sources say Keith has around two years left on his contract, and he'll be paid his salary -- around $7 million a year.

We don't know if Comcast will let Keith make a deal with another network as part of an exit agreement, but it's a good bet he'll be benched for a minimum of 6 months, and probably longer.

Keith Olbermann Abruptly Leaves MSNBC

Keith Olbermann and MSNBC are going their separate ways ... effective immediately ... the liberal cable host announced tonight in a shocking move.

MSNBC issued a statement saying they had ended its contract with Olbermann, who hosted the top rated show on the network.

The statement read in part, "MSNBC thanks Keith for his integral role in MSNBC's success and we wish him well in his future endeavors." A spokesman went on to say that Comcast's acquisition of NBC Universal had nothing to do with the decision.

Olbermann was suspended for two days in November for violating a network rule on political donations.

Lawrence O'Donnell, who hosts a show on the network at 10:00 PM, will fill Olbermann's 8:00 PM slot beginning Monday.