Strahan and his fiancée, Nicole Murphy, filmed a 38-second video for the New Yorkers for Marriage Equality campaign.
"As a defensive end for the New York Giants, I always played the game tough but fair," Strahan says in the video. "And I feel it's unfair to stop committed couples from being married."
The video closes with Strahan saying, "We believe everyone should have the right to get married."
"Just as we do," Murphy follows, while exchanging a smile with Strahan.
In recent weeks, New York Rangers forward Sean Avery and Phoenix Suns point guard Steve Nash also filmed video segments produced by Human Rights Campaign, a national organization leading the effort to legalize same-sex marriage in New York.
Nash lives in New York during the NBA offseason.
"There are a lot of tough New Yorkers, but none tougher than Michael Strahan, one of the most feared and accomplished defensive ends in history," said Brian Ellner, the HRC's senior New York strategist. "He's our Super Bowl champion for New Yorkers for Marriage [Equality].
"We are honored that he and his fiancée, Nicole, would join us in this historic fight for fairness."
In 15 seasons with the Giants, Strahan compiled 141.5 quarterback sacks, the fifth-most in NFL history. The Giants won the Super Bowl in 2007, Strahan's final season.
Murphy is the ex-wife of actor Eddie Murphy.