Anderson has closely guarded his personal life despite rumours about his sexual orientation, the Hollywood Reporter said.
"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," Anderson wrote to Daily Beast blogger Andrew Sullivan.
"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."
Cooper says he protected his privacy because it helped him in his job as a reporter but decided to come out finally.
"There continue to be far too many incidences of bullying of young people, as well as discrimination and violence against people of all ages, based on their sexual orientation, and I believe there is value in making clear where I stand," he wrote.
According to sources the network was aware of Cooper's email to Sullivan. There is no official statement from the network. Cooper is currently out of the country on assignment.