The actors portray congressional candidates who both want to represent their North Carolina district. Ferrell stars as the long-term congressman Cam Brady, while Galifianakis plays the town's Tourism Centre director named Marty Huggins.
Brady is as an education and women's rights supporter in his 'Takin' Care of Business' political ad, in which he compares Huggins's moustache to the one donned by Saddam Hussein.
Meanwhile, Huggins is described as "a small town dreamer with big town ideas" in his 'Let's Clean Up America, It's A Mess' campaign ad. The ad calls Brady "another Washington fat cat" who only knows the word "can't".
Dan Aykroyd, Brian Cox, Katherine LaNasa, John Lithgow, Dylan McDermott and Jason Sudekis also appear in the movie.
The film, directed by Jay Roach, was previously called Dog Fight and Rivals.
The Campaign will arrive in cinemas on August 10 in the US and September 28 in the UK.