Leo, 41, finally picked up his first Oscar for The Revenant on Sunday after five nominations, accepting a kiss from his proud guest for the night, mom Irmelin.
And looking like he was trying to control just how ecstatic he was, Leo told the waiting crowd in the press room how his humble beginnings in nearby east Los Angeles had made him feel somewhat of a stranger in Hollywood.
Along the awards trail leading up to the Oscars, Leo had paid tribute to his parents Irmelin and George who had supported his dream to become an actor from a young age, thanking them at the Screen Actors Guild Awards in January for "listening to an overly ambitious, slightly annoying 13-year-old kid who wanted to go on auditions every day after school, I wouldn’t be standing here without you."
He explained again on Sunday: "Look, I grew up in east Los Angeles. I was very close to the Hollywood studio system.
"But I felt detached from it my whole life, and to have had parents that have allowed me to be a part of this industry, to take me on auditions every day after school and to tell stories like this has been my dream ever since I was four years old, and this film to me was exemplary in the sense that I got to work with the director and all the things we spoke about off-camera during the making of this movie transferred their way onscreen.
"This was true storytelling. We really got to have a collaborative experience together and this was a journey that I'll never forget with Alejandro. It took up such a large portion of our lives, but as a result we have a great film to look back on for years to come."
After receiving a standing ovation from the starry crowd at the Dolby Theatre – including from a tearful Kate Winslet – Leo said he felt "very honored, quite frankly."
Fans including singer Adele had wished him luck and he said: "It all feels incredibly surreal. It’s surreal because you can't reach out and physically meet everybody. You hear it on the Internet, you hear it from other people, and the truth is, we always strive for the best in what we do, but this year in particular I've been overwhelmed with such support. Really, truly, by so many fans and so many people in the industry. It's quite shocking, actually, and what can you say except I'm very grateful. I really am."
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Most of all, Leo said, he was happy to take the chance to talk about his other passion, the environment and climate change, urging viewers "let us not take our planet for granted" in his acceptance speech, adding: "This whole thing has been an amazing experience and for me to be able to sit there and not only talk about the film but to talk about something that I am duly as obsessed with besides cinema, and that’s our environment and climate change.
"To be able to speak about that in a platform of 100s of millions of people that are watching this. To me, like I said, this is the most existential crises our civilization has ever known, and I wanted to speak out about that tonight because simultaneously while doing this brilliant film that Alejandro directed, I've been doing a documentary about climate change which has brought me to Greenland China, India to speak with the world’s leading experts on this issue and the time is now. It’s imperative that we act.
"And I really wanted tonight, I feel so overwhelmed with gratitude for what happened tonight, but I feel there is a ticking clock out there. There is a sense of urgency that we all must do something proactive about this issue and certainly with this upcoming election, the truth is this: If you do not believe in climate change, you do not believe in modern science or empirical truths and you will be on the wrong side of history and we need to all join together and vote for leaders who care about the future of this civilization and the world as we know it.”
And paying tribute to his Oscar-winning director Alejandro González Iñárritu, cinematographer Emmanuel "Chivo" Lubezk, Leo added: "It’s incredible that two outsiders like Chivo and Aljeandro came from Mexcio, came to our industry, affirm their beliefs artistically and here we have a two-time Golden Globe winner and Chivo a three-time winner. I am so proud to [be up here with you guys]… these guys represent everything about what this industry is and what it should be. I just want to congratulate you guys, it's awesome."