- The protagonist. The daughter of a drunken sailor and a woman who married beneath her, she comes to live with her wealthy uncle and aunt, Sir Thomas and Lady Bertram. They take her in as an act of charity to her parents. She is mistreated and always reminded of her "place" as a charity ward, but she eventually comes to be an indispensable member of the family. Modest, always proper, and, as she grows older, quite beautiful, Fanny is secretly in love with the Bertrams' son Edmund but is the subject of proposals by the slick Henry Crawford.
Sir Thomas Bertram
- A wealthy landowner and Fanny's uncle. He is authoritarian and rather hard on his children until a series of disasters show him the error of his ways. He owns slaves on his plantations in the Caribbean, a fact that hangs over the book. He means well and eventually does right by Fanny.
- Fanny's aunt; her mother's sister and Sir Thomas's wife. She is neurotic, a hypochondriac, and lazy. A beauty in her youth, she values people's attractiveness over all else, yet she is honest enough to admit how much Fanny means to her.
- The Bertrams' younger son. Since he will not be the heir to Mansfield, he will become a clergyman. The only one of the Bertrams' children with a good head and a good heart, Edmund is Fanny's closest companion. He rather blindly falls in love with Mary Crawford, which almost leads to his downfall.
- The Bertrams' older daughter. Vain and pretentious, she abuses Fanny and marries the odious Rushworth for his fortune. Her self-indulgence eventually gets her in quite a lot of trouble. Her name would have been pronounced "Mariah" (as in Mariah Carey).
- The Bertrams' younger daughter. She is equally vain but slightly less cocky, since she is younger and less beautiful than Maria. She follows Maria around, and, upon Maria's elopement, she runs away with Yates, her brother Tom's friend.
- The Bertrams' older son and the heir to Mansfield. He lives to party and has gotten into debt, for which Edmund will suffer. Eventually, his lifestyle catches up to him, as he nearly dies from an illness caused by too much drinking.
- Sister to Fanny's mother and Lady Bertram; wife of the first parson at Mansfield Parsonage. She has no children of her own and is an officious busybody, always trying to derive glory from her association with the family. She is horribly cruel to Fanny, whom she is always reminding of her "place" in the family.
- Sister of Mrs. Grant, who is the wife of the second parson at Mansfield. She is beautiful and charming, but also shallow and evil. She has been brought up poorly by an aunt and uncle and has been subject to the influences of her fashionable friends. She becomes friends with a reluctant Fanny, while Edmund falls in love with and nearly proposes to her.
- Mary's brother. He is equally charming and possibly even more amoral, and he possesses a sizeable estate. First Maria and Julia fall in love with him, and he takes to Maria, despite her engagement. When Maria marries and the sisters leave Mansfield, he falls for Fanny and proposes to her. Everyone is convinced he is a changed man. Eventually, he meets up with Maria again, and the two run off, but their relationship ends badly.
- Fanny's brother. Sir Thomas has gotten him a commission in the Navy, and Henry gets him a promotion as part of his effort to seduce Fanny. William and Fanny are extremely close, and he impresses everyone as a bright, capable young man. He represents a sort of ideal companion for Fanny, although, as her brother, of course, he is not an eligible mate for her.
- Maria's fiance and then husband. He is an idiot and a bore, but quite wealthy. It is his estate that the group visits early in the novel. He provides some comic relief with his stupid comments.
- Fanny's younger sister, with whom she gets reacquainted when she returns to her family's home. Susan is a diamond in the rough, a smart girl with essentially good manners who is stuck in a terrible home. Fanny brings her back to Mansfield Park with her, where she becomes a new favorite of Sir Thomas and Lady Bertram.
- Tom Bertram's friend, who proposes the amateur theatricals at Mansfield. He shows an interest in Julia, which continues in London. After Maria runs off with Henry, Julia and Yates elope and marry; they, however, are rehabilitated within the family.