Stingo is a 22-year-old Southern transplant trying to establish himself as a novelist in New York City in 1947. He lives off his modest savings in a Brooklyn boarding house after quitting his unfulfilling publishing job. Inexperienced and sexually frustrated, he observes the world with a mixture of youthful arrogance and extreme vulnerability. He quickly becomes entangled in the passionate, volatile lives of his upstairs neighbors.

Sophie is a beautiful, emotionally fragile Polish Catholic immigrant who survived the Auschwitz concentration camp. Now living in Brooklyn, she depends heavily on her lover, who rescued her from severe malnourishment and failing health upon her arrival in America. She carries a profound, crippling sense of guilt regarding her wartime actions and gradually unburdens these painful memories onto her young neighbor.

Nathan is a handsome, highly intelligent Jewish intellectual who claims to conduct biological research. He rescued Sophie from physical collapse, acting as her devoted caretaker and introducing her to American culture and classical records. However, he suffers from severe paranoia and rapid mood swings, transforming from a generous benefactor into a terrifyingly abusive partner without warning.

Stingo's father is a gentle, retired Southern gentleman farmer who recently took over a peanut farm in Virginia. Baffled by his son's desire to live in the chaotic environment of New York, he prefers the quiet stability of the South. He respects his son's literary ambitions and provides gentle guidance without forcing his own preferences.

Professor Biegański is a law professor at Cracow University and Sophie's authoritarian father. He utilizes his daughter primarily as a typist for his manuscripts, constantly belittling her intelligence. His intense political beliefs and demanding nature leave a lasting, destructive impact on Sophie's psychological development.

Mrs. Biegański is a well-educated piano teacher at the university in Cracow. She imparts a deep, lifelong love of classical music to her daughter. In her household, she is completely self-effacing, yielding entirely to her husband's aggressive personality.

Casimir is a mathematics student at the university who marries Sophie prior to the war. His primary motivation in the marriage is his admiration for his mentor, Sophie's father, leading to a respectable but largely passionless union.

Jan is Sophie's young son who is transported to the concentration camps alongside his mother and sister. Securing his safety becomes the singular, desperate focus of Sophie's existence while she suffers through the horrors of her imprisonment.

Eva is Sophie's eight-year-old daughter. She accompanies her mother and brother on the agonizing train transport to the camps, representing the ultimate innocence destroyed by the war.

Höss is the coldly efficient commandant of Auschwitz. He treats the mass extermination of prisoners as a mundane logistical challenge rather than a moral crisis. He utilizes Sophie for her language skills, making him the target of her desperate attempts to secure better conditions for her family.

Larry is Nathan's brother and a practicing physician. He deeply understands the dangerous complexities of his brother's mental state and periodically intervenes, attempting to keep Nathan stable and relying on others to help monitor the situation.

Leslie is a highly educated young woman from a wealthy Brooklyn Heights family. She speaks openly and provocatively about sexuality and psychology, leading Stingo to heavily anticipate a romantic encounter that ultimately ends in frustration.

Mrs. Zimmerman is the pragmatic landlady of the boarding house where the central characters reside. She maintains a lenient attitude toward her tenants, allowing them to host companions of the opposite sex provided they remain reasonably discreet.

Morris is a fellow tenant in the Brooklyn boarding house. He acts as an early warning system for Stingo, expressing deep suspicion regarding Nathan's erratic behavior and comparing him to a dangerous, uncontrollable monster.

Farrell is a fellow employee at the publishing house who befriends the young Stingo. Grieving the wartime loss of his own son, who shared Stingo's literary ambitions, he offers heartfelt parting advice to encourage Stingo's writing.

Wanda is an active fighter in the Home Army resistance movement. She attempts to draw Sophie into her dangerous underground work and later reunites with her under dire circumstances in the prison system.

Dürrfeld is a German businessman who initially presents himself as a cultured academic peer in Cracow. Years later, he takes control of the entire Auschwitz complex as a portly, middle-aged industrialist who no longer recognizes the people from his past.