"I am stunned," Lemon wrote on Twitter, saying he was told by his agent he had been let go.
CNN said it "parted ways" with Lemon, who co-hosted its morning show, saying "we wish him well".
It follows on-air remarks by Lemon in which he said Republican Nikki Haley, 51, was not "in her prime".
The dismissal also comes on the heels of another major US media departure. Just moments before Lemon's announcement, Fox News announced it was parting ways with primetime host Tucker Carlson.
