The actor visited Downing Street to discuss the troubled Darfur region with Gordon Brown, 57, and his wife Sarah.
George, who is a United Nations messenger of peace, asked the PM for his support to bring stability to the area.
'I am grateful for the leadership George Clooney has shown in drawing attention to this crisis. This is a humanitarian tragedy of colossal proportions and the world must take note and act,' the PM tells the Daily Express.
The 46-year-old actor has kept busy while on his whirlwind tour of the capital.
On Monday night he partied into the early hours with Mariella Frostrup, 45, Thandie Newton, 35, and Jemima Khan, 34, at a dinner thrown in his honour at London's L'Atelier de Joel Robuchon restaurant.
And last night he was in Leicester Square for the premiere of his latest movie Leatherheads, with co-star Renee Zellweger, 38.
George was greeted by hundreds of screaming fans.