Amaechi, a center who spent five seasons with four teams, is scheduled to appear on ESPN's Outside the Lines on Sunday, and his autobiography, Man in the Middle, will be released Feb. 14.
"He is coming out of the closet as a gay man," Amaechi's publicist Howard Bragman said Wednesday.
NBA commissioner David Stern said a player's sexuality is not important.
"We have a very diverse league. The question at the NBA is always 'have you got game?' That's it, end of inquiry," he said.
Three years after his playing career ended, Amaechi has become the sixth professional male athlete from one of the four major American sports (NBA, MLB, NFL, NHL) to publicly discuss his homosexuality.
Former NFL running back David Kopay came out in 1977, and offensive lineman Roy Simmons and defensive lineman Esera Tuaolo came out more recently. Glenn Burke, an outfielder in the 1970s, and Billy Bean, a utility player in the 1980s and 1990s, also have come out.