In a statement released on Twitter, the actor said: “I feel overwhelming gratitude for the incredible people who have supported me along this journey.
“I can’t begin to express how remarkable it feels to finally love who I am enough to pursue my authentic self.”
He has asked that his pronouns are he and they, and announced his name change from Ellen to Elliot.
As well as expressing joy at his announcement, he also expressed fear at the backlash he may face.
"My joy is real, but it is also fragile” he explained, “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.
"To the political leaders who work to criminalise trans health care and deny our right to exist and to all of those with a massive platform who continue to spew hostility towards the trans community: you have blood on your hands.
“You unleash a fury of vile and demeaning rage that lands on the shoulders of the trans community, a community in which 40% of trans adults report attempting suicide.
"Enough is enough. You aren’t being “cancelled,” you are hurting people.
"I am one of those people and we won’t be silent in the face of your attacks.”
Elliot was nominated for an Oscar in 2007 for his role in the movie Juno.