The political thriller also stars Ryan Gosling.
Clooney, who also produced, directed, and co-wrote the movie, plays a politician whose career could be ended by a scandal.
Some other familiar faces include Marisa Tomei and Philip Seymour Hoffman.
The film's subject led to an obvious question on the red carpet. Would Clooney like a future in politics?
"It would never be something I'm interested in. I'm not good at the kind of compromises that you have to make to get elected. My father ran for congress, I watched that happen and I watched how frustrating it was for him and I didn't enjoy it," said Clooney.
"The Ides of March" opens in theaters this weekend.