Heard is best known for her roles in "Zombieland" and "Pineapple Express."
UsMagazine.com said the actress attended Saturday's Gay and Lesbian Alliance Against Defamation's 25th anniversary party with her girlfriend of two years, photographer and artist Tasya van Ree.
"GLAAD is one of the many reasons that I, as a 24-year-old, can come out," RadarOnline quoted Heard as saying.
"She is beautiful," Heard said of her partner. "I mean, you'd have to be crazy not to want to go out with her!"