The Bell Jar opens in the summer of 1953. Esther Greenwood is a bright nineteen-year-old working as an editorial intern at a popular women's magazine in New York City. Despite her academic promise and ambition, Esther feels isolated from society and discouraged about her future. These early symptoms of depression are aggravated by the pressure she feels to conform to social expectations of what a young woman should be – a virgin until marriage, and after marriage, a wife and a mother. Chided by her boss for not having a clear career focus, Esther goes on a series of dates, the last of which ends with her date attempting to assault her. Esther escapes, and returns home the next morning to her mother's house in the suburbs outside Boston.
As the events of the summer unfold, Esther frequently flashes back to her problematic relationship with her on-and-off boyfriend Buddy Willard, a medical student. Through these flashbacks, we learn that while Esther idolized Buddy at first, she became disillusioned when he revealed that he had a sexual affair. Later, Esther visited Buddy while he was confined to a sanitarium for tuberculosis. After rejecting his proposal of marriage, Esther followed Buddy to the ski slopes, where she had an accident and broke her leg.
Back with her mother, Esther finds out that she did not get accepted into a summer creative writing program, after which she quickly spirals down into a suicidal depression. Esther consults Dr. Gordon, but he botches her electroshock therapy, after which Esther's behavior grows increasingly erratic. Finally, Esther decides to end her life. She hides away in a crawlspace under her home and swallows a bottle of sleeping pills. Fortunately, she is rescued a few days later. After staying at a couple of hospitals, Esther is taken to a private psychiatric institution, where she meets Dr. Nolan, a compassionate female doctor. While there, Esther undergoes a series of successful electroshock and insulin therapy sessions. At the institution, she encounters Joan, a high school friend who also dated Buddy.
However, Esther's life is again threatened when, after a sexual encounter with a professor she meets in Cambridge during a visit out of the institution, she hemorrhages. Joan, who is now living in Cambridge, helps Esther to the emergency room, and Esther returns to the institution the next day. Joan also returns to stay at the institution, and commits suicide near the institution's grounds soon after. Esther's condition, on the other hand, improves. The novel ends in the winter of 1954 as Esther enters her exit interview, which will determine if she's ready to leave the institution.