He was fired, when he deliberately used biased resources that told a totally untrue story, in his zeal to "bring down" George W. Bush. He refused to verify the "information" he was given by democrat operatives, put the story on the air, and then it all turned out to be false.
It came out that HE, and he alone decided to use that material, and that he had made no effort at all to verify the information. Then, the network began checking a bunch of other stories he had done, and discovered a long history of biased reporting, of making up stories, and of changing stories around to suit his political biases. That was when CBS fired him.
He tried suing the network, and he lost, big time, plus he was required to pay all of their legal expenses. He appealed, and lost again. he tried to take the case to the US Supreme Court, and they refused to hear his case.
It cost him over 4 million dollars, and he ended up with egg on his face, a destroyed reputation and not much else.
His son Chris appears to be following in his fathers much earlier footsteps, when Mike Wallace still had integrity.