A-list actor Leonardo DiCaprio has formally accepted his appointment as United Nations representative on climate change on Saturday evening in New York City.

In a brief ceremony held at the U.N. Headquarters in New York, DiCaprio received a pin and a special certificate from U.N. Secretary-General Ban Ki-Moon to mark the honor.

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The "Wolf of Wall Street" star reportedly attended the event with his parents.

DiCaprio said he was very honored and pleased to accept the role as U.N.'s Messenger of Peace On Climate Change.

"To be an ambassador on peace, in particular on the issue of climate change, is a great honor. Thank you so much for bestowing this honor, Mr. Secretary-General," the 39-year-old actor said.

"I and so many people believe, it (climate change) is the most important issue of our time," he added.

In a statement released early this week, DiCaprio said he would use his new role to campaign for environmental issues and to raise awareness on climate change.

"I feel a moral obligation to speak out at this key moment in human history - it is a moment for action," the actor said.

"How we respond to the climate crisis in the coming years will likely determine the fate of humanity and our planet," he added.

Ban, on the other hand, hailed DiCaprio as a "credible voice in the environmental movement," saying the actor can amplify the message on climate change.

"I am pleased he has chosen to add his voice to U.N. efforts to raise awareness of the urgency and benefits of acting now to combat climate change," the U.N. chief noted.

In 1998, the Academy Award-nominated actor established the Leonardo DiCaprio Foundation to protect the Earth's biodiversity and ecosystems.

Since then, he has been involved in the climate change advocacy through campaigning, grant-making, and media projects.

With the appointment, the actor now joins the likes of actresses Angelina Jolie and Emma Watson, both of whom were tapped to represent different organizations in the U.N.

On Sunday, DiCaprio and actor Mark Ruffalo are set to join the Peoples' Climate March, wherein more than 100,000 people are expected to march through the streets of Manhattan as a part of the U.N.'s global campaign on climate change.

Organizers aim to make the September 21 event the largest march for climate action in history.