"I didn't set out to be the first openly gay athlete in a major American team sport. But since I am, I'm happy to start the conversation," Collins said in an interview with Sports Illustrated.
Collins, 34, a Los Angeles native, is currently a free agent after 12 seasons in the NBA. The 7-foot center has played for six teams, including the Boston Celtics and most recently the Washington Wizards.
Former President Bill Clinton was among the first to congratulate Collins.
"I have known Jason Collins since he was Chelsea's classmate and friend at Stanford," Clinton said. "Jason's announcement today is an important moment for professional sports and in the history of the LGBT community. It is also the straightforward statement of a good man who wants no more than what so many of us seek: to be able to be who we are; to do our work; to build families and to contribute to our communities."
Collins is now the first active male player in any of the four major professional U.S. sports to come out as gay.
"We met with him last summer and I was very impressed him with as a person," said Bulls coach Tom Thibodeau. "Two close friends of mine coached him, and they raved about him as a person, as a player, as a leader, so I didn't think it was a big deal. In today's society, that's normal, so I was very impressed with him and my opinion of him hasn't changed one bit. I'm happy for him."
"His decision to come out is saving lives, when you have 30-40 percent LGBTQ youth who have considered suicide," said Tom Elliott, public relations director at the Center on Halsted in Chicago. "That's a significant rate higher than their straight peers."
Collin says he has been considering coming out for the past couple of years but made the decision to do so after the Boston bombings.
"He kind of witnessed that going on," said SI writer Franz Lidz, "and life changes in an instant, and he doesn't want to remain closeted his whole life
Brian Kupersmit is the president of Chicago Metropolitan Sports Association, the largest gay and lesbian sports organization in the Midwest. He says Collins' decision to come out as gay is courageous and hopes it won't negatively impact his chances of getting signed by another team or getting endorsement deals.
"I'm imaging that Jason reached a point in his life where he felt like it was more important to him to be authentic, to be himself, to be who he is," said Kupersmit. "And I believe he's hoping he can pursue his passion as well, and I'm optimistic he'll be able to do that."
Support has been pouring in for Collins. NBA Commissioner David Stern said, "Jason has been a widely respected player and teammate throughout his career and we are proud he has assumed the leadership mantle on this very important issue."
Collins has also been commended by the White House. White House spokesman Jay Carney called Collins' decision courageous and said the administration views it as another example of progress and evolution in the U.S. as Americans grow more accepting of gay rights and same-sex marriage.
The Associated Press contributed to this report.