The main characters of Three Soldiers are John Andrews, Dan Fuselli, and Chris Chrisfield. Each of them adapts differently to army life. None of them are initially bad characters, yet they all end up disillusioned or doing bad things as a result of their experience in the army during WWI. The characters reflect the attitude of the author's "lost generation" with its pacifism, distrust of authority and dissatisfaction with mainstream American life.

John Andrews is a well-educated New Yorker and aspiring composer who comes to the war as an idealist seeking to further a worthy cause. He is put off by the dreary routines and regimentation of military life, and his sense of independence makes it difficult for him to submit to authority. He uses his sense of humor to cope. His sense of independence finally gets the better of him toward the end of the war when he deserts the army in Paris to study music, live with his French girlfriend, and compose his Opera. He is arrested by an MP and serves a prison sentence.

Dan Fuselli is a working-class private from San Francisco who is ambitious for promotion in the army. He is cunning and willing to submit to the authority of the officers in order to get ahead. He is a less appealing character in the story than Andrews and his willingness to play by army rules does not lead to anything close to his desired promotion. He also ends up disillusioned.

Chris Chrisfield is another everyman character, like Fuselli. In this case, he a good-natured farm boy from Indiana. When he is bullied by a superior he is unable to control his anger which then colors his subsequent army career. In the heat of battle he takes his revenge by fragging the bully with a hand grenade. He gets away with the murder and his main concern is getting caught and facing the consequences. He is another disillusioned casualty of war in the eyes of the pacifist author, Dos Passos.