Tris Prior is the main protagonist of the novel. She is sixteen, blond, short, and thin. Despite her small frame, she has a powerful personality and a strong desire to help others. The first two novels in the series show how tough Tris is, especially when she chooses Dauntless as her faction, but Allegiant shows her softer side and her ability to change her mind and adapt to new situations and information. Unlike Tobias, who struggles with his new identity, Tris takes what she learns at the Bureau and refuses to let it change how she sees herself. She knows who she is and what she stands for, but Tris is also willing to adapt and see things from varying perspectives. Her adaptability allows her to help defeat the Bureau and make amends with Tobias. However, Tris also has a strong intuition and often follows her gut, which usually turns out to be correct, making her a great leader whom others follow without hesitation.

Although capable of fighting her way through any situation, Tris strongly desires to make her parents proud. The more Tris learns about Natalie at the Bureau, the more she wants to make a home at the Bureau to feel that connection with her mother.