Aunt Polly, sister to Tom Sawyer's late mother, serves as guardian to Tom and his half-brother Sid, while also caring for her daughter Mary. She disciplines the children, frequently quoting Scripture, using methods like strikes with her thimble and verbal scoldings, portrayed as less severe than others' punishments. She struggles to balance her duty to correct Tom's misbehavior—skipping school, sneaking out, or stealing jam—with her deep affection for him, admitting an inability to punish him harshly despite frustration.

She extends consistent kindness and compassion, particularly towards the marginalized. After Tom and Huckleberry Finn return from their supposed deaths, she embraces Huck and publicly offers him familial love, calling him a "poor motherless thing." Her affectionate gestures, including kisses for Tom, alleviate his low spirits and restore his happiness.

Her relationship with Tom involves mutual affection alongside attempts to outwit each other. She employs leading questions to expose his lies, such as detecting unauthorized swimming by examining his shirt collar thread. Tom feels greater remorse when she cries over his actions than when facing physical punishment, indicating their strong bond. The narrative suggests their similar natures contribute to this dynamic, with both employing clever tactics in their interactions.

Superstitions and folk remedies, like belief in "miracle cures," inform her behavior. She maintains a role representing the orderly adult world, contrasting with the children's adventurous sphere.