The 41-year-old actor, a long time environmental activist, joined the President and climate scientist and professor Katharine Hayhoe in a panel discussion at the South by South Lawn festival, an arts event held in the White House grounds on Monday (03Oct16).
Leonardo was promoting his new documentary film Before the Flood, in which the actor travelled around the world talking to scientists, world leaders and people affected by climate change in a bid to highlight the issue.
Opening the talk, The Revenant star delivered an uncompromising challenge to politicians who doubt the science of climate change.
"If you do not believe in climate change, you do not believe in facts or in science or empirical truths," Leonardo said. "And therefore, in my humble opinion, you should not be allowed to hold public office."
However the actor praised President Obama as a politician, "who has done more to create solutions for the climate crisis than any other in history."
All three panelists struck a downbeat tone, with Obama admitting, "We're on the more pessimistic end of what was possible" in terms of adopting anti-climate change measures.
The Hollywood superstar even joked that he might be planning on escaping Earth, saying that he'd signed up for a trip to Mars before telling the audience he'd cancelled.
Directed by Leonardo's friend, the actor and documentary filmmaker Fisher Stevens, Before the Flood received its U.S. premiere at the South by South Lawn festival on Monday (03Oct16). It will hit cinemas on 21 October (16).