The Moneyball star will join Steve McQueen's forthcoming film, which also stars Michael Fassbender and Chiwetel Ejiofor, The Playlist reports.
Based on an 1853 autobiography, Twelve Years A Slave centres on Solomon Northup, a black man who was tricked into slavery by two men pretending to be circus promoters. He ultimately won his freedom with the help of a Canadian white carpenter.
Pitt will also produce the project through his Plan B company.
The actor is currently shooting the zombie film World War Z. The set of the movie was recently raided by Hungarian officials, who confiscated 85 weapons "because they were not fully inoperable as they were supposed to be".
Pitt and Fassbender previously appeared in the film Inglourious Basterds together.
Filming on Twelve Years a Slave is expected to begin in 2012.
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Watch Brad Pitt in the Moneyball trailer below: