The 39-year-old "Wolf of Wall Street" star will help promote global action on climate change, according to the Associated Press.
He'll be joining other Hollywood UN Messengers like George Clooney and Michael Douglas
The Hollywood star was selected not only for his consistence as one of the world's leading actors' but also for his established commitment to environmental causes.'
DiCaprio established a foundation in 1998 with a mission to promote the Earth's last wild places and build a more harmonious relationship between humanity and the natural world.
The secretary-general said DiCaprio will address next Tuesday's climate summit where he expects a some of 120 world leaders.