"I'm an out, proud and happy gay man," Herndon told People.
"I have an awesome relationship that I've been in for a good number of years," Herndon says in the "Entertainment Tonight" interview, which will air Thursday evening. "[I] love him very much and he loves me." Herndon also said that he hopes to marry and have children.
Herndon, 52, told People that he first thought he might be gay when he was just 10 years old, and began telling friends when he was 20. But he married and divorced and says both ex-wives knew he was gay.
"I have made a lot of mistakes in my life. They've been my mistakes, and I own them," the singer tells People. "I've done a lot of work around forgiveness with people that I've hurt and people I've not been honest with because of my sexuality."
Although Herndon has not posted on Twitter or Instagram about his announcement, fans took to his latest Instagram photo, an image featuring Herndon and former reality star Camille Grammer, to share reactions to the news.
"So glad you can truly start to live your life now," wrote one. "Lies and deceit are such a heavy burden to (bear), no matter the secret . Have always loved (your) music and looking forward to more."
He also believes his industry will understand his news.
"Traditionally in country music, we don't see a lot of support for the LGBT community, but that's changing so much," he told "Entertainment Tonight," adding, "I get to be free today. I'm born again today, and I feel like I'm not gonna have any trouble sleeping tonight."
Herndon was nominated for a 2011 Grammy Award for Best Southern, Country or Bluegrass Gospel album.