Jason Collins, who became the National Basketball Association's first openly gay player, retired aged 35 but vowed he would continue the fight to make US sports more tolerant.
Collins, who played 22 games for the Brooklyn Nets last year, announced his decision on Wednesday in an article for Sports Illustrated, writing that "basketball saved me".
"In order to understand why I am so lucky to be sitting here today as a person who is finally comfortable in his own skin, you need to understand how basketball saved me," Collins wrote.
"I needed to live the past few years as an openly gay basketball player in order to be at peace retiring today."
Collins was not on an NBA roster this season.
Following Collins' coming out, US college football player Michael Sam revealed in February that he too was gay.
"Congrats to @jasoncollins98 on the end of a long and successful career. Wishing you the best on what's to come next, I know it'll be great," Sam wrote on Twitter.
Collins said he would encourage other gay athletes in North America's professional sports to come out.
"There are still no publicly gay players in the NFL, NHL or major league baseball," Collins wrote.
"Believe me: they exist. Every pro sport has them. I know some of them personally.
"When we get to the point where a gay pro athlete is no longer forced to live in fear that he'll be shunned by teammates or outed by tabloids, when we get to the point where he plays while his significant other waits in the family room, when we get to the point where he's not compelled to hide his true self and is able to live an authentic life, then coming out won't be such a big deal.
"But we're not there yet."
Collins became the first openly gay NBA player when he took the floor for a February 23 game against the Los Angeles Lakers.
"Among the memories I will cherish most are the warm applause I received in Los Angeles when I took the court in my Nets debut, and the standing ovation I got at my first home game in Brooklyn," Collins added. "It shows how far we've come."
Collins also thanked his teammates and coaches on the Nets for their support.
"There are so many people I have to thank for helping me on my journey. My teammates, coaches, and the Brooklyn Nets organization gave me an opportunity," he said.
In 13 NBA seasons, Collins averaged 3.6 points and 3.7 rebounds in 735 games with six different teams. He was a member of two NBA finals teams.
Source: AFP