DiCaprio was named best actor at the 88th Academy Awards.
The Revenant received six nominations.
DiCaprio received a standing ovation, after five acting nominations and one nomination as producer of best picture nominee Wolf of Wall Street.
The star thanked Revenant director Alejandro González Iñárritu and co-star Tom Hardy for his “fierce talent on screen” before calling for action to combat climate change, saying making The Revenant was “about man’s relationship to the natural world”.
“Climate change is real – it is happening right now,” he said “It is the most urgent threat facing our species, and we need to work collectively together and stop procrastinating.”
He asked the audience to “support leaders around the world who do not speak for the big polluters or the big corporations but who speak for all of humanity, for the indigenous people of the world, for the billions and billions of underprivileged people who’ll be affected by this”.
“Let us not take this planet for granted. I do not take tonight for granted.”
It has been 22 years since he was first nominated for an Academy Award, after best supporting actor for What’s Eating Gilbert Grape.
DiCaprio said, speaking to reporters: “I feel very honoured, to share this has been an amazing experience, to sit there and talk about the film.
“I also got to talk about something I have been obsessed with – the environment and climate change – on a platform with hundreds of millions of people watching worldwide.”