Scoot McNairy and Anthony Mackie are also on board.
David Gordon Green is directing with George Clooney and Grant Heslov producing through their Smokehouse Pictures banner, with Bullock exec-producing.
The film is based on the 2005 documentary of the same name, which focuses on the use of American political campaign strategies in South America.
Peter Straughan penned the script. Courtenay Valenti and Racheline Benveniste are overseeing for the studio.
Production is set to start this fall.
Dowd was last seen in HBO’s “The Leftovers” and Showtime’s “Masters of Sex” and was also recently seen in the Fox Searchlight pic “The Drop.” She is repped by Innovative Artists and Principal Entertainment.