The 46-year-old actor has been campaigning for an end to the 4 1/2-year war in Darfur and for humanitarian aid for the millions caught up in the conflict. He will become the ninth U.N. peace envoy.
While many U.N. agencies have goodwill ambassadors to promote activities ranging from helping children and refugees to promoting human rights, "messengers of peace" are selected by the secretary-general to promote the broader work of the United Nations.
U.N. spokeswoman Michele Montas said Clooney was recognized "for focusing public attention on crucial international political and social issues."
As a messenger of peace, he will have "a special focus on United Nations peacekeeping," Montas said.