The Oscar-nominated star of Juno has announced that he is transgender, introducing himself as Elliot Page in a social media post.
The Canadian-born actor, formerly known as Ellen Page, said he could not "begin to express how remarkable it feels to finally love who I am enough to pursue my authentic self".
"I love that I am trans. And I love that I am queer," he wrote on Twitter.
Page also used the post to address discrimination towards trans people.
"The truth is, despite feeling profoundly happy right now and knowing how much privilege I carry, I am also scared. I'm scared of the invasiveness, the hate, the 'jokes' and of violence," the 33-year-old wrote.
"To be clear, I am not trying to dampen a moment that is joyous and one that I celebrate, but I want to address the full picture. The statistics are staggering."
Addressing the trans community, Page said he would "do everything I can to change this world for the better".
Page received international acclaim for starring as a pregnant teenager in the 2007 film Juno.
Other major films include Inception and the X-Men series, while the actor has more recently starred in Netflix series The Umbrella Academy.
Page came out as gay in 2014, telling an audience in Las Vegas: "I am tired of hiding and I am tired of lying by omission."
The actor, who is married to choreographer Emma Portner, has been a prominent advocate for LGBT rights.
Trans people across the UK have told me that Elliot Page's coming out has happened at a "much needed time".
This news, from one of Hollywood's biggest stars, who now becomes one of the world's most famous transgender stars, has happened on a big day for trans rights in the UK.
Today, a legal case about puberty-blocking drugs concluded, with leading charities calling it a "rolling back" of trans rights, and "a catastrophic moment" for trans people.
In Elliot Page's statement, he referenced how he will now fight for better trans healthcare.
Since coming out as gay in 2014, Page has become known as one of Hollywood's most outspoken LGBT actors. In his viral speech in 2014, he said "I suffered for years because I was scared to be out… And I'm standing here today, with all of you, on the other side of all that pain."
Today's coming out has triggered another huge international wave of support.
Many praised Page following his announcement on Tuesday.
"Elliot Page has given us fantastic characters on-screen, and has been an outspoken advocate for all LGBTQ people," said Nick Adams, director of transgender media at advocacy group GLAAD.
"He will now be an inspiration to countless trans and non-binary people. All transgender people deserve the chance to be ourselves and to be accepted for who we are. We celebrate the remarkable Elliot Page today."
"So proud of our superhero," Netflix wrote on Twitter.