Lara Jean is a shy, imaginative 16-year-old high school junior who spends her weekends baking and hanging out with her sisters. She prefers romantic fantasies over real-world dating, processing her intense crushes by writing secret love letters she keeps hidden in a hatbox. As her older sister leaves for college, Lara Jean faces the responsibility of stepping up in her tight-knit family. Her quiet life shifts dramatically when her private letters are mysteriously mailed to her past crushes.

Peter is a popular, athletic high school student known for his charm and good looks. He recently experienced a messy breakup with his girlfriend, Genevieve. Behind his confident exterior, he demonstrates surprising thoughtfulness and a protective nature. He proposes a fake relationship with Lara Jean to solve both of their current social dilemmas, slowly showing a more grounded personality beneath his outgoing reputation.

Margot is the pragmatic, responsible eldest Song sister who took over running the household after their mother died. She acts decisively and avoids dwelling on the past. Before moving to Scotland for college, she chooses to break up with her longtime boyfriend to focus on her education. She sets a standard of perfection that her younger sisters measure themselves against, maintaining a stoic front to lead her family.

Josh is the boy-next-door neighbor who has grown deeply integrated into the Covey family over the years. He relies on their household as a refuge from his parents' frequent arguments. After Margot ends their relationship, he feels untethered and confused. He seeks comfort in his ongoing friendship with Lara Jean while trying to figure out his changing status within the family.

Kitty is the youngest and most outspoken of the three Song sisters. She holds grudges fiercely and acts impulsively, but also protects her family with intense loyalty. She longs for a pet dog and slowly adjusts to a household routine managed by Lara Jean rather than Margot. Her actions often force her older sisters to confront truths they would rather avoid.

Genevieve is a wealthy, socially powerful high school student who recently ended her relationship with Peter Kavinsky. She holds a longstanding grudge against Lara Jean, her former best friend from middle school. She actively guards her territory and uses gossip to handle perceived threats to her social standing, creating major obstacles for Lara Jean.

Dr. Covey is a dedicated father and gynecologist raising his three daughters alone following his wife's passing. He attempts to keep the girls connected to their late mother's Korean heritage by occasionally cooking traditional meals. He provides a loving, stable environment, though his daughters often hide their teenage struggles from him to avoid causing him extra stress.

Chris is Lara Jean's best friend. She is known for her rebellious streak and outright disregard for school rules. She smokes, skips class, and contrasts sharply with Lara Jean's rule-abiding nature. Despite her flighty tendencies, she acts as a loyal confidant and provides Lara Jean with unfiltered advice and access to high school gossip.

Lucas is a kind, observant classmate who receives one of Lara Jean's accidentally mailed letters. Rather than making the situation awkward, he handles the revelation gracefully. He provides Lara Jean with a safe space to talk and models how to establish boundaries regarding personal identity.

John Ambrose is a former friend and middle school crush of Lara Jean who moved away. As one of the recipients of her secret love letters, he represents a safe, uncomplicated romantic possibility from her past, free of the daily drama of her current high school life.

She is the maternal grandmother to the Song sisters. She visits during major holidays and gently encourages their father to start dating again, bringing a traditional, maternal presence to the household that the girls deeply respect.

Owen is Peter's younger brother. He lives with Peter and their mother following his parents' divorce, and he looks up to his older brother for guidance in their altered family dynamic.