(CNN) -- It's the biggest move of his career and it's off the court.
Jason Collins, who played with the NBA's Washington Wizards this season, has disclosed that he is gay, making him the first active openly homosexual athlete in the four major American pro team sports. The center, who is now a free agent, made the disclosure in a column appearing in the upcoming issue of Sports Illustrated.
"Jason Collins has forever changed the face of sports," said the Human Rights Campaign, a civil rights group fighting for gay rights.
It likened the announcement to Jackie Robinson, the first African-American to play in major league baseball in the modern era.
"At a time when millions are reflecting on the life and legacy of Jackie Robinson, Jason Collins is a hero for our own times," the group said.
Collins is a 7-foot center who played with six NBA teams over the past 12 seasons. Along with the Wizards, they are the Boston Celtics, Minnesota Timberwolves, New Jersey Nets, Atlanta Hawks and Memphis Grizzlies. NBA Commissioner David Stern said the 34-year-old veteran is widely respected in the league.
"We are proud he has assumed the leadership mantle on this very important issue," he said in a statement.
Washington Wizards President Ernie Grunfeld said the team is "extremely proud of Jason and support his decision to live his life proudly and openly."
"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."
Fellow NBA players tweeted support for Collins including Kobe Bryant and Baron Davis.
Collins played his college ball at Stanford University. Chelsea Clinton, the daughter of former President Bill Clinton and a Stanford alumna, wrote on Twitter that she is "very proud of my friend Jason Collins for having the strength & courage to be the first openly gay player in the NBA."
Bill Clinton called the announcement an "important moment for professional sports and in the history of the LGBT community."
Collins, who played for the Celtics this season before being traded to the Wizards, wrote in his essay that U.S. Rep. Joe Kennedy, D-Massachusetts, helped prompt his decision to come out as gay. Kennedy and Collins were roommates at Stanford. He recounts hearing about Kennedy, who is not gay, marching in Boston's Gay Pride Parade.
"For as long as I've known Jason Collins he has been defined by three things: his passion for the sport he loves, his unwavering integrity, and the biggest heart you will ever find," Kennedy said. "I'm proud to stand with him today and proud to call him a friend."
A few athletes have come out as gay after they've left professional sports. One is John Amaechi, a former NBA player.
Amaechi told CNN he hopes Collins will be a catalyst for a wider acceptance of openly gay athletes, saying he believes Collins is better equipped than anyone who came before him to handle the attention that will come his way. But it may take more, Amaechi said.
People like to believe one iconic figure can change things, he said, "but the reality is that when there's this tipping point, or enough people coming together deciding that change is necessary, that's when change happens."
In 2005, Sheryl Swoopes -- a top player in the WNBA, the women's pro league -- announced she was gay.