Mansfield Park tells the story of protagonist Fanny Price as she navigates her adolescence and young adulthood. As a child, Fanny is sent to live with her aunt, Lady Bertram, and her uncle, Sir Thomas, at their country estate, Mansfield Park. Mrs. Price, Fanny’s mother and Lady Bertram’s sister, is of a lower class and struggles financially due to her poorly chosen marriage to naval officer Mr. Price. Together they have too many children to care for, so Lady Bertram, Sir Thomas, and Fanny’s other aunt Mrs. Norris contrive to take in Fanny, who is her eldest daughter.
At Mansfield, Fanny grows up with her four cousins: Tom, Edmund, Maria, and Julia. When Fanny first arrives at Mansfield, she is uncomfortable because of her lack of proper manners and exposure to luxury and wealth. She is homesick and misses her brother William, with whom she is extremely close. In Fanny’s early years at Mansfield, her relations generally neglect her, and Mrs. Norris is downright tyrannical and verbally abusive in how she treats her niece. Only her cousin Edmund goes out of his way to make Fanny feel comfortable, establishing an intense bond between them.
As Fanny grows older, she begins to feel more used to the lifestyle at Mansfield. Fanny serves as a companion to Lady Bertram, and stays at home with her reclusive aunt when the rest of the family leaves to socialize. Mrs. Norris’s husband Mr. Norris eventually dies, causing Mrs. Norris to move out of the Parsonage and into a house nearby. Normally, Edmund should have inherited his fortune, but Tom, who has a gambling problem, must use the money set aside to pay back his debts. A new preacher, Dr. Grant, moves into the Parsonage with his wife, Mrs. Grant.
Sir Thomas leaves for business in Antigua, and, frustrated by his son Tom’s lack of responsibility, takes him along. Maria, meanwhile, attracts the attentions of the rich but stupid Mr. Rushworth, and they begin a courtship. Mr. Rushworth asks for Maria’s hand in marriage, and she and Sir Thomas both agree to it, on the condition that they wait until Sir Thomas returns from the West Indies to wed.
That summer, Mrs. Grant’s half siblings, Mary and Henry Crawford, come to stay with her. They are both attractive and charming, and they quickly befriend the Bertrams. Tom returns from the West Indies, with Sir Thomas to follow in the late fall. Henry flirts with both Julia and Maria, despite Maria’s engagement. Together, the Bertram children, the Crawfords, and Fanny make a trip to Mr. Rushworth’s estate, where Henry focuses his flirtation on Maria, leaving Julia feeling dejected. Meanwhile, Mary and Edmund begin to develop a romantic feeling between them. This upsets Fanny, who, over the years, has come to love Edmund as more than just a cousin.
The young people decide to put on a play after hearing about Tom’s friend, Mr. Yates, doing the same at another party. Edmund and Fanny resist, saying it would not be proper, but eventually Edmund joins in. Fanny, however, holds out. Maria and Henry continue to flirt. Edmund and Mary fall deeper in love, and Fanny experiences intense pain watching them perform the love scenes. They make all the preparations for the play, but Sir Thomas returns from Antigua just before it is ready. He is angry at them, thinking the theatrics are totally improper, and puts an end to the fun.
Maria, who had hoped Henry would ask to marry her, gives up her dreams and marries Mr. Rushworth. She and Julia go to Brighton together with him, and then to London. Mary becomes closer with Fanny. With the other young women gone, Henry decides that, as a game, he will try to seduce Fanny. Fanny, meanwhile, is still secretly in love with Edmund, and is caught in the middle of Mary and Edmund’s romance, which is a constant source of pain. Edmund tries to determine if Mary would marry him, but Mary is unwilling to commit because Edmund is a younger son, fortuneless, and a clergyman.
Fanny’s brother William comes to visit, and Sir Thomas, who has warmed to Fanny since his return from Antigua, throws a formal ball in her honor. Henry has not succeeded in his sport of seducing Fanny, but has accidently fallen in love with her while trying. He leaves for London, where he secures a promotion for William in an attempt to win Fanny’s heart. He then proposes to Fanny, who rejects him, much to Sir Thomas’s disapproval. Not long afterward, Fanny returns to her childhood home in Portsmouth for the first time in many years. Fanny loathes Portsmouth, but becomes close with her younger sister, Susan.
Henry visits Fanny at Portsmouth and reiterates his affection for her. Fanny begins to warm up to him, and Mary encourages her to marry him. Soon afterward, however, Fanny receives word that Tom is gravely ill. She worries and longs to return to Mansfield. Then, Fanny hears rumors that Henry and Maria have run away together. In a letter, Edmund confirms the rumors, and adds the news that Julia and Mr. Yates have eloped. Fanny returns home to Mansfield and brings her sister Susan with her.
When Edmund talks to Mary about the affair between Maria and Henry, she does not condemn their actions, but rather complains about the fact that they were found out. As a result, Edmund is disgusted and terminates his relationship with her, much to Fanny’s delight. Henry is totally excommunicated from the Bertram household. Maria, now disgraced, leaves Mansfield to live in a house far away with Mrs. Norris. Julia and Mr. Yates attempt to make amends with Sir Thomas and are forgiven. The Grants and Mary move away from Mansfield, settling in London. Edmund thinks about Fanny for the first time as a romantic option, and eventually falls in love with her. They marry and lead a happy life together.