Cain, 74, first went to an Atlanta hospital for treatment on July 1, his staff had said.
His death was announced on Herman Cain's website and Facebook page.
"Herman Cain – our boss, our friend, like a father to so many of us – has passed away," the statement on his website said, noting there were "hopeful indicators" in recent days that he'd recover but adding: "And yet we also felt real concern about the fact that he never quite seemed to get to the point where the doctors could advance him to the recovery phase."
Newsmax, which Cain recently joined, also posted an obituary confirming he died Thursday. Cain also was a Fox News contributor for years.
Former Cain staffer Ellen Carmichael tweeted Thursday morning: "I’m very saddened to learn of the passing of my former boss, Herman Cain. I’m bracing for the cruelty online about how he deserved to get COVID and die because of his politics. We’re living in a dark time. But, they didn’t know him. I did." Read more at FOX News