The 45-year-old won the Best Actor category against Leonardo DiCaprio (Once Upon a Time in Hollywood), Adam Driver (Marriage Story), Antonio Banderas (Pain & Glory), and Jonathan Pryce (The Two Popes).
"I do not feel elevated above any of my fellow nominees because we share the same the love of film and this form of expression has given me the most extraordinary life," he said during his acceptance speech. "I don’t know what I’d be without it ... I’ve been a scoundrel in my life. I’ve been cruel at times, hard to work with. Many of you in this room have given me a second chance."
Phoenix also touched on representation, racism, inequality, and animal rights in his speech. "Whether we’re talking about gender inequality or racism or queer rights or indigenous rights or animal rights, we’re talking about the fight against the belief, one nation, one race, one gender or one species has the right to dominate, control and use and exploit another with impunity," the actor said. "I think that we’ve become very disconnected from the natural world and many of us, what we’re guilty of is an egocentric world view, the belief that we’re the center of the universe."
He previously earned a Golden Globe and BAFTA for his portrayal as Arthur Fleck/Joker.
Check out Phoenix's speech below.
Phoenix is the the second actor to win an Academy Award for his role as the Clown Prince of Crime. Heath Ledger received a posthumous Best Supporting Actor prize at 2009 Oscars for The Dark Knight.