Briony is the thirteen-year-old youngest child of the wealthy Tallis family. Highly imaginative and fiercely precocious, she spends her time writing stories to manufacture the adult complexities she desperately wants to understand. Her intense desire for maturity and order deeply clouds her perception of the real-world events unfolding on her family's country estate.

Robbie is the son of the Tallis family's cleaning lady and lives in a cottage on their property. Having recently graduated from Cambridge University with the financial backing of Jack Tallis, he holds strong ambitions to attend medical school. He is intelligent and hardworking, though he constantly bumps against the rigid social class barriers separating him from the Tallis family.

Cecilia is a recent Cambridge graduate who feels entirely directionless after returning to her family's sprawling country home. As the middle Tallis child, she often navigates the unspoken tensions of her household while repressing her own complicated emotions. Her frustrations manifest as a defensive irritation, particularly when dealing with her lifelong companion, Robbie.

Paul is a wealthy aristocrat and the heir to a large confectionary business who visits the Tallis family. He carries a profound sense of elite entitlement and views the impending war purely as a business opportunity to sell low-quality chocolate to the military. He uses his high social status and wealth to insulate himself from accountability and social rules.

Lola is the fifteen-year-old cousin of the Tallis children. Sent to the estate while her parents undergo a bitter divorce, she brings a dramatic flair and acts as an uneasy surrogate guardian to her younger twin brothers. She frequently clashes with Briony, asserting her slight age advantage to project an aura of absolute maturity.

Leon is the eldest Tallis sibling. He maintains a cheerful, uncomplicated outlook on life and deliberately avoids taking on heavy responsibilities or dealing with serious household conflicts. He enjoys a strong bond with Cecilia and serves as the family's main link to high-society London circles.

Emily is the matriarch of the Tallis family. Her chronic migraines frequently isolate her from the daily workings of the household, leaving her children largely unsupervised. She maintains strict emotional stoicism, choosing to silently bear her suspicions about her husband's activities rather than confront him directly.

Jack is the patriarch of the Tallis family who spends the vast majority of his time working in London. He remains a distant authority figure in his children's lives, functioning mostly as a financial provider who funds Robbie's education while avoiding domestic matters.

Jackson is one of Briony's nine-year-old cousins staying at the Tallis estate. Deeply homesick due to his parents' impending divorce, he struggles to adapt to the unfamiliar environment of the country house and seeks comfort in his older sister.

Pierrot is the nine-year-old twin brother to Jackson. Like his brother, he suffers from severe homesickness while seeking refuge at the Tallis estate during his parents' divorce, eventually plotting to run away in hopes of returning home.

Danny is the son of the Tallis family's driver. He is transitioning into adulthood and helps around the estate with physical labor, drawing occasional observation from Cecilia regarding his suddenly mature features.

Corporal Mace is a British soldier navigating the chaotic retreat to Dunkirk alongside Robbie. Despite holding a higher military rank, he often defers to Robbie's practical knowledge of the French countryside and relies on him for translation.

Corporal Nettle is a soldier traversing the war-torn landscape of France. He attempts to keep Robbie grounded and focused on survival as their group battles exhaustion and the constant threat of attack.

Luc is a severely wounded French soldier brought to the London hospital where Briony trains. Drifting in and out of consciousness, he seeks comfort from his nurses in his final moments, mistaking Briony for someone from his past.

Sister Drummond is an authoritarian nursing instructor managing the wartime hospital wards. She maintains strict discipline among the young trainees while attempting to coordinate the chaotic influx of wounded soldiers returning from France.

Fiona is a loud, jolly trainee nurse who works directly alongside Briony. She attempts to keep her friend grounded and socially engaged despite the grueling hours and the looming dread of the war surrounding them.