In the futuristic city of dystopian Chicago, society is divided into five factions: Abnegation (the selfless), Amity (the peaceful), Candor (the honest), Dauntless (the brave), and Erudite (the intellectual). The remaining population are the Factionless, who have no status or privilege in this society. When children reach the age of 16, they undergo a serum-induced psychological aptitude test which indicates their best-suited faction, but they are allowed to choose any faction as their permanent group at the subsequent Choosing Ceremony.
Beatrice Prior (Shailene Woodley) was born into Abnegation, which runs the government. Her father, Andrew Prior (Tony Goldwyn), serves on the ruling council along with the head of Abnegation, Marcus Eaton (Ray Stevenson). Beatrice takes her test with a Dauntless woman, Tori Wu (Maggie Q), as her proctor. Her results show equal attributes of multiple factions, which means that she is Divergent. Her divergence includes Abnegation, Erudite, and Dauntless. Tori records her results as Abnegation, warns her to keep the true result a secret, and says that because Divergents can think independently and are aware of any serums injected into them, the government cannot control them and considers them to be threats to the existing social order.
The next day, at the Choosing Ceremony, Beatrice's brother Caleb (Ansel Elgort) chooses Erudite, and after some hesitation, Beatrice chooses Dauntless. After the ceremony, Beatrice meets Christina (Zoë Kravitz), Al (Christian Madsen), and Will (Ben Lloyd-Hughes), three other initiates from other factions who also chose Dauntless. Christina and Al are from Candor, and Will is from Erudite. The initiates' commitment and fearlessness are immediately tested, and Eric Coulter (Jai Courtney), a brutal Dauntless leader, makes it clear that anyone not meeting the high expectations of Dauntless will be expelled from the faction to become Factionless. Beatrice is the first to volunteer for a leap of faith from a tall building into a dark hole and lands into a net. When Four (Theo James), a transfer initiates' instructor, asks her name, she decides to shorten it to "Tris" so she can leave her earlier identity behind.
Tris initially struggles in Dauntless training and ranks far below the cutoff after the first evaluation, but with Four's help, she slowly improves. After Eric matches her against her nemesis, Candor transfer Peter Hayes (Miles Teller), in a fight, Tris is soundly defeated and ends up in the infirmary. When she discovers that she will miss the most important test, Capture The Flag, she leaves the infirmary, joins the other initiates, secures her team's victory, and makes the final cut. In the next phase of training, the initiates are subject to psychological simulations in which they face their worst fears. Tris's divergence allows her to excel at the tests, which she solves by unusual ways, but Four warns her to hide her abilities and to solve the challenges as a normal Dauntless would, as Divergents can also manipulate tests and serums. Tris visits Caleb, who tells her that Erudite is planning to overthrow Abnegation and become the ruling faction. On her return to Dauntless headquarters, Tris is attacked by Al, Peter, and Drew before she is rescued by Four. The next day, Al pleads with Tris for her forgiveness but she refuses and calls him a coward. He later kills himself by jumping into "The Chasm," rather than live with the shame.
To prepare her for the final test, Four takes Tris into his own fear simulations in which she learns that his real name is Tobias Eaton, the son of Marcus Eaton. After the simulation, they kiss. Tris then passes her test and is officially initiated into Dauntless. The rest of the Dauntless are injected with a serum supplied by Erudite, which is supposedly for tracking but actually for mind control. The next morning, the Dauntless prepare to execute Abnegations under orders of the Erudites. As Divergents are unaffected by the new serum, Tris must blend in to avoid suspicion. She finds Four, who reveals himself as a Divergent. When the Dauntless move to raid Abnegation, Tris and Four separate from the group and attempt to locate Tris's parents, but Eric realizes that Four is not under control and captures both of them. Four is taken into custody, and Tris is ordered to be executed. Her mother, Natalie (Ashley Judd), appears and saves her but is shot and killed as they try to escape.
Tris finds her father in hiding with Caleb, Marcus, and several Abnegation members. The group sneaks into Dauntless headquarters, where Tris encounters Peter and forces him to lead them to Erudite's control center. Her father sacrifices himself in a shootout, and Tris goes in alone to find Four, who is now under stronger mind control, which is designed for Divergents, and attacks her. Using her knowledge of his fears, she manages to wake him from the mind control, and both enter the central control room, where the Erudite leader Jeanine (Kate Winslet) is about to have the Dauntless army execute the entire Abnegation faction. Tris uses a sample of the mind control serum on her to force her to cancel the program. The group escapes the compound and boards a train out of the complex.