But Clooney was blocked from delivering a message on his recent trip to Darfur to a meeting of nations contributing peacekeeping troops.
Diplomats said several countries including Russia had objected to his presence as inappropriate.
"The message is the world is watching and that at this point we cannot afford to fail"
Instead, Clooney delivered the message to a news conference, telling reporters: "The message is the world is watching and that at this point we cannot afford to fail."
"Millions are homeless, not from famine or disease or acts of God, but from a well armed militia intent on ridding the land of its people."
Clooney said his new role was to raise awareness about UN peacekeeping efforts generally and he would "go wherever I have to to bring some attention."
"We tend to not get to see enough of what we need to see anymore," he said, adding: "It seems as if at times celebrity can bring that focus."
"It can't make the policies, it can't change people's minds really, but you can bring a camera where you go because they'll follow you and you can shine a light on it. That seems to be my job."
Clooney is the UN's ninth messenger of peace – a position appointed from people prominent in the art, music, literature and sports worlds who have agreed to help focus attention on UN work.
The program was started in 1998 by the then UN secretary-general, Kofi Annan.