In an article in Sports Illustrated, Collins says, "I'm a 34-year-old NBA center. I'm black. And I'm gay."
The Los Angeles native, who is now a free agent after finishing this past season with the Washington Wizards, said that he's happy to start the conversation.
"I wish I wasn't the kid in the classroom raising his hand and saying, 'I'm different.' If I had my way, someone else would have already done this. Nobody has, which is why I'm raising my hand," Collins says.
The 7-foot-tall Collins has played for six teams in his 12-year NBA career, making the playoffs nine times, including two NBA finals.
"We are extremely proud of Jason and support his decision to live his life proudly and openly," said Washington Wizards President Ernie Grunfeld on behalf of the team. "He has been a leader on and off the court and an outstanding teammate throughout his NBA career. Those qualities will continue to serve him both as a player and as a positive role model for others of all sexual orientation."
Collins played his high school ball at Harvard-Westlake School, along with his twin brother, Jarron Collins, before going to Stanford University. Their former coach at Harvard-Westlake, Greg Hilliard, said he's happy for Jason.
"While we were surprised, we also feel like there couldn't be a better person to take on that responsibility and role. We're extremely proud of him," said Hilliard.
In the Sports Illustrated article, Collins says he was once engaged to a woman, thinking he needed to marry her and raise kids with her.
"He would come back and introduce me to a girl he was dating. So obviously that had to be difficult for him. But it was all about his fear of losing all this that he had and putting up appearances," said Hilliard.
Soon after the article was published, Los Angeles Lakers star Kobe Bryant showed his support in a Tweet that said, "Proud of @jasoncollins34. Don't suffocate who u r because of the ignorance of others #courage #support #mambaarmystandup #BYOU."
Collins says he quietly made a statement for gay rights even while keeping his sexual orientation a secret. He wore No. 98 with the Celtics and Wizards - 1998 was the year that Matthew Shepard, a gay college student in Wyoming, was killed, and the Trevor Project, a suicide prevention organization, was founded.
"All the support I have received today is truly inspirational," Collins said in a Tweet. "I knew that I was choosing the road less traveled but I'm not walking it alone."
The Associated Press contributed to this report.