Collins is the first current player in the four biggest sports -- baseball, basketball, football and hockey -- to announce he is gay.
"I didn't set out to be the first openly gay athlete playing in a major American team sport," Collins wrote in the article posted on SI's website. "But since I am, I'm happy to start the conversation. If I had my way, someone else would have already done this. Nobody has, which is why I'm raising my hand."
Collins is listed as a co-author of the article that begins: "I'm a 34-year-old NBA center. I'm black. And I'm gay."
Collins writes that he dated women and was engaged at one point. He also said he thought about openly revealing to being gay during the 2011 NBA player lockout.
Collins said he told his twin brother, Jarron, who is also an NBA player, last summer about his sexual orientation.
Collins spend his college career at Stanford and was the 18th overall selection by Houston in the 2001 NBA draft. A draft-day trade sent him to the New Jersey Nets where he played for more than six seasons. He also played for Memphis, Minnesota and Atlanta. He played a total of 38 games for Boston and Washington in the 2012-13 season. He is currently a free agent.