The CNN journalist has long been the subject of rumours about his sexuality, but refrained from ever broaching the subject publicly.
Cooper opened up about his sexuality in a letter to The Daily Beast's Andrew Sullivan in response to a recent Entertainment Weekly article about the emergence of gay celebrities coming out of the closet.
"I've always believed that who a reporter votes for, what religion they are, who they love, should not be something they have to discuss publicly. As long as a journalist shows fairness and honesty in his or her work, their private life shouldn't matter," Cooper insisted.
His statement continued: "Recently, however, I've begun to consider whether the unintended outcomes of maintaining my privacy outweigh personal and professional principle... 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.
"I have always been very open and honest about this part of my life with my friends, my family, and my colleagues. In a perfect world, I don't think it's anyone else's business, but I do think there is value in standing up and being counted. I'm not an activist, but I am a human being and I don't give that up by being a journalist."
Read Cooper's full email here.
The journalist has said in the past the he avoided speaking out about his personal life after seeing his mother Gloria Vanderbilt hounded by the tabloids.
His sexuality has been an open secret in some media circles, with Out ranking him as the second most powerful gay man in the US in 2007.
Cooper could comment further on his revelation on tonight's Anderson Cooper 360, which airs at 8pm ET on CNN in the US.