Frederic Henry: Frederic is the central character and first-person narrator of the story. Everything that happens in the novel happens to him and he relates his experiences to the reader with detached and detailed descriptions. He is a young American architecture student who joins the Italian ambulance corps for want of something better to do during the First World War. He serves at the rank of lieutenant. We know little of his personal history before coming to Italy except that he receives money from his grandfather and feels no strong ties to his family. He is a heavy drinker but sober minded.
Catherine Barkley: Catherine is the lead female character in the novel. She is the literary representation of Sister Agnes von Kurowsky, an American nurse who spurned Hemingway's affections when he was recovering from wounds suffered in Italy. Catherine is an English nurse who recently lost her fianc´┐Ż of eight years in the Battle of the Somme, an experience that has affected her mental health. She doesn't think much of the Italian front or of the Italian army, but she falls in love with Frederic who soon thereafter falls in love with her. She becomes pregnant with his child and dies during childbirth in Switzerland.
Lieutenant Rinaldi: Rinaldi is Frederic's best friend at the start of the novel. He is an Italian army surgeon whose main concerns are for his work, drinking, and whoring. He is boisterous, friendly, and very fond of Frederic. At the start of the novel, he and Frederic share a similar outlook on the world. As Frederic becomes more emotionally involved with Catherine, he and Rinaldi, though still friends, become distanced from one another. He frequently refers to Frederic as "baby". When Frederic last sees him, Rinaldi believes that he has contracted syphilis. He has become cynical about the war and suffers from overwork.
The priest: Though we never learn his name, the priest is initially a timid man from a simple mountain village serving in the Italian army. He and Frederic share a burgeoning friendship. The lewd officers at the nightly mess constantly harass him, but as the story progresses, he becomes more confident and sure of his place. He suggests to Frederic the idea that love is the desire to serve.
Helen "Fergy" Ferguson: Fergy is a Scottish nurse who is Catherine's best friend. She and Frederic share a mutual distaste for one another until Catherine suggests to Frederic that Fergy is only jealous because they have found love and she has not.
Count Greffi: The Count is a former diplomatic servant for both Austria and Italy. He is 94 years old and it is obvious from the narrative that Frederic values his opinion. He and Frederic share a game of billiards while Frederic is in Stresa. It is at this time that the Count suggests that love for a woman is on par with religious devotion.