"The fact is, I'm gay, always have been, always will be, and I couldn't be any more happy, comfortable with myself and proud," he wrote in a letter to Andrew Sullivan of the Daily Beast.
Cooper, the son of heiress and designer Gloria Vanderbilt, had long been the subject of rumors about his sexual orientation. But he said he wanted to retain some privacy for personal and professional reasons.
"It's become clear to me that by remaining silent on certain aspects of my personal life for so long, I have given some the mistaken impression that I am trying to hide something," Cooper said.
Cooper said he was not trying to push an agenda or become an activist.
"I've never wanted to be any kind of reporter other than a good one, and I do not desire to promote any cause other than the truth," he said. "I still consider myself a reserved person and I hope this doesn't mean an end to a small amount of personal space. But I do think visibility is important, more important than preserving my reporter's shield of privacy."
The Associated Press contributed to this report.