Redford is also directing the film, which will begin shooting later this month.
The Matthew Michael Carnahan-scripted film focuses on the intersecting events that follow two soldiers getting separated from their platoon in Afghanistan. According to Variety, Luke will play one of the soldiers.
Redford is in place as a college professor, with Cruise playing a senator and Streep as a reporter. Michael Pena ("World Trade Center") will also co-star.
Luke earned strong reviews for his performance in this fall's drama "Catch a Fire." Since being discovered and cast in the lead of "Antwone Fisher," his credits have included "Glory Road" and "Friday Night Lights."