According to Variety, the 39-year-old, known for roles in Savages, True Detective and Friday Night Lights, will play Ben Edwards, best friend of Pratt's James Reece.
The series follows Reece, a Navy SEAL who returns home to his family after his entire platoon is ambushed during a mission. Reece has trouble remembering the events of the ambush and soon uncovers a conspiracy that reaches the highest levels of government.
Kitsch recently starred as David Koresh in Paramount Network's series Waco. Pratt is best known for his role as Peter Quill in the Guardians of the Galaxy movies, Owen Grady in Jurassic World and as Andy Dwyer in Parks and Recreation.