The 26-year-old actress came out in front of a conference for LGBT youth presented by the Human Rights Campaign. The video was posted to YouTube.
"I suffered for years, because I was scared to be out. My spirit suffered, my mental health suffered and my relationships suffered. And I'm standing here with all of you on the other side of that pain," Page said.
Page was nominated for an Oscar for her 2007 role in "Juno," and she delved into the world of dreams in "Inception."
Page says this announcement is aimed at kids without the advantages of fame.
"Maybe I can make a difference to help others have an easier and more hopeful time. Regardless for me, I feel a personal obligation and a social responsibility," Page said. "Thank you for inspiring me, thank you for giving me hope. Please keep changing the world for people like me. Happy Valentine's Day. I love you."
Page's announcement was so popular on the Human Rights Campaign website that it actually crashed the server. Her name was also trending on Twitter, with many people offering their support.
Lance Bass tweeted, "We love you @ellenpage!!"
Actress Holland Taylor tweeted, "So happy about @EllenPage What a generation! Wait till everyone in this age group runs things. A kinder sharper more humane & human society."
Page simply tweeted, "Thank you [Human Rights Campaign] and everyone for all the love and support."