The political comedy stars the pair as rival North Carolina politicians vying for a seat in congress.
Released by Empire, the posters show Ferrell in character as Cam Brady, a congressman left vulnerable by his own PR error, and Galifianakis as Marty Huggins, the outsider who takes advantage.
Jay Roach (Austin Powers, Meet The Parents) has directed from a script by The Other Guys writer Chris Henchy and Eastbound & Down scribe Shawn Harwell.
A trailer for The Campaign was released last month.
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The Campaign is released in the US on August 10 and on September 28 in the UK. Watch a promotional video for Ferrell's character below: