Pitt, 51, was seen in a rugged soldier look, wearing grey army camos and combat boots to add to his new hair, reported E! online.
Netflix's satirical comedy is inspired by Michael Hastings' memoir "The Operators: The Wild and Terrifying Inside Story of America's War in Afghanistan".
The "Fury" actor will reportedly play the character based on Stanley McChrystal, the controversial general who commanded US armed forces in Afghanistan.