Phoenix took the opportunity to speak for the 'voiceless' saying: "I think we've become very disconnected from the natural world... we feel entitled to artificially inseminate a cow and when she gives birth we steal her baby... and I think we fear the idea of personal change because we think we have to sacrifice something to give something up."
He continued: "I think that when we use love and compassion as our guiding principles we can create and develop... I have been a scoundrel in my life, I've been selfish, I've been cruel at times, hard to work with and I'm grateful that many of you have given me a second chance."
Then he finished by paying tribute to his late brother, River, adding: "When he was 17 my brother wrote this lyric: 'run to the rescue with love and peace will follow'."
The actor scooped the award for his starring role in the film, beating the likes of Leonardo DiCaprio (Once upon a time... in Hollywood) and Adam Driver (Marriage Story).
The film, which is directed and written by Todd Phillips (The Hangover), is a dark, standalone that looks into the life of Batman's arch nemesis.
Phoenix plays the troubled Arthur Fleck, a struggling clown who is cast aside by society and spirals into the depths of madness, eventually becoming the infamous Clown Prince of Crime and commencing his campaign of terror against the people of Gotham.
The film was an absolute smash hit at the box office as it managed to rake in more than $1 billion (£775m) worldwide. That's even more impressive when you consider that it only cost $62.5m (£48.4m) to make.
The 45-year-old actor has also received praise for his decision to wear the same tuxedo for every event he's turned up to during awards season, in a bid to reduce waste.
He partnered with legendary designer Stella McCartney, who revealed the arrangement from the actor in a post on Instagram.
Stella wrote: "This man is a winner. Wearing custom Stella because he chooses to make choices for the future of the planet. He has also chosen to wear the same tux for the entire awards season to reduce waste. I am proud to join forces with you."
Featured Image Credit: Warner Bros