In a near future where Earth is under assault by an alien species called Mimics, Major William Cage, a public affairs officer with no combat experience, is deployed to join a massive Allied invasion in France against the extraterrestrials. Despite his attempts to avoid the front lines, Cage is thrust into battle and quickly killed. However, in a bizarre twist of fate, he finds himself caught in a time loop, forcing him to live out the same brutal combat and die again and again. With each iteration, Cage becomes more adept at fighting the aliens, learning the patterns of battle.

During one time loop, Cage encounters Sergeant Rita Vrataski, known as the "Angel of Verdun" for her heroism in a previous battle against the Mimics. Rita recognizes Cage's time-looping ability as a tool they can exploit to win the war and trains him to fight more effectively. As Cage continues to loop, he and Rita develop a plan to use his unique situation to locate and destroy the aliens' power source, a hive-mind entity referred to as the Omega, which is responsible for the Mimics' ability to manipulate time and outpace humanity's strategies in war. Together, they embark on a perilous quest, fighting against both the Mimics and the dwindling time to alter the course of the conflict.