The book "Suicide of a Superpower" contained chapters titled "The End of White America" and "The Death of Christian America." Critics called the book racist, anti-Semitic and homophobic, charges Buchanan denied.
MSNBC President Phil Griffin said last month that he didn't think Buchanan's book "should be part of the national dialogue, much less part of the dialogue on MSNBC."
The network said on Thursday that "after 10 years, we have decided to part ways with Pat Buchanan. We wish him well."
Buchanan, in a column posted on Thursday, called the decision "an undeniable victory for the blacklisters."
The former GOP candidate had seemed increasingly out of place on MSNBC as it emphasized liberal commentary in recent years. But he kept a regular presence, even forging an unlikely chemistry with talk show host Rachel Maddow despite disagreeing on most issues.
Buchanan wrote that advocacy groups like Color of Change and the Anti-Defamation League brand people as racists or anti-Semites if they dare "to venture outside the narrow corral in which they seek to confine debate." They seek to silence and censor dissent while proclaiming devotion to the First Amendment, he said.
"I know these blacklisters," he wrote. "They operate behind closed doors, with phone calls, mailed threats and off-the-record meetings. They work in the dark because, as Al Smith said, nothing un-American can live in the sunlight."
The liberal media watchdog Media Matters for America said that MSNBC made the right decision in letting Buchanan go.
The book "was not his first, nor his worst offense," said Ari Rabin-Havt, executive vice president of Media Matters. "He's been making the same racially insensitive, anti-Semitic and homophobic statements for the past 50 years."