The Oscar nominee plays a lesbian parent in The Kids Are Alright, but she told CNN that her support for gay parents preceded her work on the movie.
"It's something I've believed in for a long time," she said. "People ask if I think that movies influence popular culture, and yes, in a way, but I always say that movies more often reflect popular culture. A movie like this can't exist if it's not something that's already happening all across the United States."
She continued: "There are so many gay families - so many two moms and two dads - and very normal, very idiosyncratic, really regular American families happening all over the place."
Moore added that she teaches her own children that heterosexual and same-sex couples deserve to be treated equally.
"The fact that this movie exists is really a way to recognise that. In my life and in my children's lives, gay families are just part of the fabric of their world. We know plenty of families with two moms and two dads, and you know, they're just the same as we are."
The Kids Are Alright is now playing in US cinemas and is released in the UK on October 29.
