The AFL has expressed support for same-sex couples being allowed to marry in a development advocates hope will help build momentum for marriage equality.

AFL chief executive Gillon McLachlan revealed the league's stance on the polarising issue in response to a letter from Geelong woman Sharyn Faulkner, who has a gay son.

"If the AFL publicly declares that they are in support of marriage equality you will give that young player who is struggling with their sexuality the courage to realise just who they are," Ms Faulkner wrote.

In response, Mr McLachlan wrote that football was no place for homophobia, and gave his personal commitment to "continue to speak out in this area whenever I can."

"The AFL will keep saying no matter how many times it takes, that our game does not tolerate discrimination in any form, be that sexual identity, gender, race (or) religious views ... we also support the position of marriage equality for all people.