During initiation, he met Tris, Christina, and Albert, mainly because he wasn't friends with Edward and Myra and didn't want to be a third wheel to the couple. These four constantly fought against Peter Hayes, Drew and Molly Atwood.
In the first stage of initiation, he was paired against Al in their first fight. Will teased that Al was a slowpoke before the latter struck a blow to Will, knocking him out cold and securing Al the win. Al helped carry Will to the Medical Ward to recover.
As his old faction begins to spread falsified reports about Abnegation and Tris's family, Will works to keep Tris calm, letting her vent her frustrations and stepping in to prevent a fight breaking out. Often he would go along with Christina's attempts to cheer Tris up, such as tearing up the reports and throwing them into the Chasm.
On Visiting Day, his sister Cara paid a visit to him. When he introduced Tris to his sister, Cara treated the pair coldly, accusing Tris' mother of hoarding goods for the Abnegation, based on the reports published by Jeanine. Angered, Tris threatened to punch Cara, but Will intervened.
After the rankings are posted for the second stage of initiation, Peter proposes that Tris has been playing all of them – pretending to be weak when she is really aiming to edge them out of Dauntless. As he and Christina have fallen drastically in the rankings, Will struggles with the thought that Peter could be right, despite Tris's protests that she's not trying to fool them. He, Christina, and Al isolate Tris briefly, which results in the latter spending more time with Uriah and the Dauntless-born. Following Peter, Drew, and Al's attempt to throw Tris into the Chasm one night, Will patches up their friendship and accompanies Tris everywhere in an effort to protect her.
During the mind-control simulation of the Dauntless and Erudite against the Abnegation, Will unknowingly went after Tris and she shot him in the head out of self-defense. Although she deeply regretted her actions, she had no other choice.
Will is first shown standing in the same train car as Peter and Albert, jumping off the train before Christina and Tris. He asks Eric if there is water or some other safety measure in place after the initiates jump off the roof into the Dauntless compound, the latter shrugging off his question. He is formally introduced over dinner when he explains the Abnegation diet to Christina as the reason for Tris reacting strangely to the hamburgers in front of them. Christina and Al throw sarcastic remarks at him when he comments on Candor's flaw of saying anything and everything that comes to mind, which he endures without offense. He observes Tris trying to strike up a conversation with Four about his past before sharing with the other transfers what he's heard about Four.
In the first stage of initiation, Will is scored high, due to his skills with fighting and weapons. He tries to help Tris during gun training, telling her that she will hit the target at least once, even if by accident. (Based on statistics.) Will witnesses Tris standing in for Al when Four throws knives at her during their knife training. He congratulates Tris for standing up to Eric before noticing Jeanine Matthews approaching their group with other Erudite members. He ducks his head to avoid eye contact with Jeanine, observing as the latter talks to Tris about her faction change. He finds it curious but Tris shakes it off as nothing, explaining that she ran into Jeanine prior to the Choosing Ceremony.
After Tris loses her second fight, he and Christina visit Tris in the Medical Ward before leaving to play Capture the Flag. He attempts to reason with Tris who is distraught at the news of being kicked out of initiation at Eric's orders – suggesting that maybe Tris could return to Abnegation due to her father's position on the counsel. Despite her injuries, Tris makes the train and is welcomed by Christina and Will, who help her get set up for Capture the Flag. They are placed on the same team with Four as their leader. He argues with the other teammates about a strategy as Tris and Four scale the Ferris wheel to scout out the other team's location. Once Tris locates the other team's area, he and the other members act as cover, shooting neuro darts at Eric's team while Tris and Christina retrieve the flag.
As the second stage of initiation begins, Will undergoes his fears in a simulation with the other transfers. While his timing isn't mentioned, it is implied that he took a long time get out of his fears compared to Tris. Peter falsely congratulates Tris on her speed before demanding to know what her secret or trick is to getting out of the simulation quicker. Will defends her and Peter shoots back that Tris is close to edging him and the others out of the faction. Despite his friend's insistence that she doesn't know how or why she is faster in the simulations, Will begins to doubt Tris, isolating himself from her. They become friends again after Al commits suicide, due to guilt in participating in Peter's plan to throw Tris into the Chasm.
After completing his final test, Will celebrates with Christina and Tris upon learning they will remain in Dauntless. The next morning he falls under the control of the simulation injected into his neck the day before, following the others to the Abnegation sector of town. Tris encounters him while escaping from Eric and Max, the latter firing at her despite her pleas for him to stop. Resigned to the fact that he can't break from the simulation, Tris is forced to shoot Will in the head, killing him.
In the book, Will was described as a blonde with shaggy hair and a crease between his eyebrows. Physically, he was pale and solid, with an easy smile and green eyes the color of celery that glinted with mischief and light. His hand was bigger than Tris's shoulder blade and his teeth were white and straight.
In the film, Will is slightly shorter than Al with dark brown hair and dark eyes.
The pair met during the early days of initiation. At first, Will and Christina often engaged in light banter during their conversations, disagreeing with one another. (Ex. Keeping a dog as a pet.) Eventually their time spent together resulted in the pair becoming close and developing feelings for each other. Towards the end of initiation, he and Christina talked by the trains when he stopped and kissed her. They continued talking as if nothing had happened, which Christina enjoyed. Then, Christina kissed him like nothing happened. When they found out that they both got into Dauntless, they kissed passionately not caring who saw them.
In Insurgent, Christina found out that Tris had been the one who shot Will during the latter's trial conducted by Candor. Upset by the revelation, Christina did not speak to Tris for days, privately mourning the loss of her boyfriend. Eventually, she forgave Tris when she realized that there really was no other option and that he was under the simulation.
Will befriended Tris during the early part of initiation, commenting that she was defying the statistics by missing the target during shooting practice. Eventually he shared meals with Christina, Al, and Tris in an effort to separate himself from Edward and Myra, who shared little in common with him. At times he would tease Tris for exhibiting behaviors and traits typical of Abnegation people when she witnessed things like public affection. He was protective of Tris, likely due to the fact that she was the smallest transfer and seemed vulnerable in front of their fellow initiates. (Peter, Drew, and Molly)
When his former faction began attacking Abnegation and Tris's family in the news reports, Will often acted as a voice of reason, pulling Tris out of the room and trying to get her to calm down. While he listened to her frustrations about false information being spread, he admitted that he understood his former faction's frustrations and what they wanted changed in the government. During one of these incidents, he shared that he left his former faction as he found them dull and arrogant.
When Peter planted the idea of Tris cheating or using a trick to get through her fears quicker, Will began to express doubts about his friend's true intentions, isolating himself from her briefly. They patched things up when Tris revealed that Peter, Drew, and Al attempted to hang her over the Chasm in a kidnapping attempt.