The CNN journalist wrote in an online letter that he had kept his sexual orientation private for personal and professional reasons, but came to think that remaining silent had given some people a mistaken impression that he was ashamed.
"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 the letter, published by Andrew Sullivan of the Daily Beast.
Cooper, the son of Gloria Vanderbilt, had long been the subject of rumors about his sexual orientation. He said that in a perfect world, it wouldn't be anyone's business, but that there is value in "standing up and being counted."
"I still consider myself a reserved person and I hope this doesn't mean an end to a small amount of personal space," he wrote. "But I do think visibility is important, more important than preserving my reporter's shield of privacy."
CNN said it would not comment, and that Cooper was on assignment and there were no plans for Cooper to discuss it on the air.
Few national television news reporters have publicly acknowledged being gay, with MSNBC's Rachel Maddow and CNN's Don Lemon perhaps the best known.
Cooper's show, "Anderson Cooper 360," received an award this year from the Gay and Lesbian Alliance Against Defamation.
"Even prior to coming out publicly, Anderson's terrific work has raised awareness of inequalities facing LGBT people, said GLAAD President Herndon Graddick. "He's a role model to millions and now will inspire countless others."