It is 1950s New York City and Tom Ripley is a young man struggling to make a living, relying on his talents to get by. While at a recital where he plays the piano, Tom is approached by wealthy ship builder Herbert Greenleaf, who mistakenly thinks he went to Princeton, due to the borrowed Princeton blazer Tom is wearing. Greenleaf recruits Ripley to go to Italy to persuade his rebellious son Dickie to return home to the United States. In return for this he will pay Ripley one thousand dollars. Despite never having met Dickie and never having attended Princeton, Ripley accepts.
Upon arriving in Europe, Ripley meets Meredith Logue, a young, wealthy heiress to a textile empire. During their brief conversation Ripley impulsively introduces himself as Dickie. Shortly thereafter he fakes a chance encounter with the real Dickie and his fiancé Marge Sherwood, attempting to convince Dickie that they met at Princeton. Subsequently he visits Dickie and Marge and discloses that Dickie's father paid him to persuade Dickie to come home. Dickie is furious and suggests Ripley return to America to inform his father he has no intention of going home. Rather than doing this, Ripley insinuates himself into Dickie's life, citing a mutual love of jazz. The two devise a scheme to con additional money from Mr. Greenleaf by mailing regular letters stating that Dickie is vacillating and can likely be persuaded to return if Ripley remains in Italy and continues to apply pressure on him.
While on an excursion to Rome, Ripley meets Freddie Miles, a friend of Dickie's who barely conceals his contempt for Ripley. A local Italian girl whom Dickie had gotten pregnant drowns herself after he refuses to support her financially. This precipitates a downward spiral for Dickie and leads him to resent Ripley's constant presence, which he finds suffocating. Ripley is becoming sexually obsessed with Dickie and also growing attached to the high-flying lifestyle his friendship with Dickie affords him. Before Ripley returns to America Dickie invites Ripley on a sailing trip to San Remo where he is house hunting. While they are at sea Ripley suggests that he should come back to Italy the following year and become Dickie's housemate. Dickie informs Ripley he is going to marry his fiancé Marge, which enrages Ripley so much he lashes out at him and hits him repeatedly with an oar, killing him. Panicking, Ripley tries to conceal the murder by scuttling the boat with Dickie's body on board then swims to shore himself.
When the hotel concierge mistakes him for Dickie, Ripley realizes that he can assume Dickie's identity. He forges his signature, alters his passport and begins funding his lifestyle using Dickie's trust fund. He writes to Marge using Dickie's typewriter and convinces her he has left her. He creates an elaborate charade that maintains both his own and Dickie's identities, checking into two separate hotels under their respective names, and passing messages between hotel staff members to make it appear that Dickie is still living. The situation becomes all the more complicated when Meredith Logue re-emerges, still under the false impression that he is Dickie.
Ripley rents a large apartment and spends Christmas alone having gifted himself many expensive presents. Meanwhile Freddie tracks Ripley down, fully expecting to find Dickie. Upon arrival, he is suspicious that the apartment is not furnished in Dickie's style. Ripley has adopted Dickie's hairstyle and mannerisms. As Freddie is leaving the apartment, he meets the building's landlady, who says that she loves to hear piano music coming from the apartment where Dickie is supposed to live. Freddie knows that Dickie does not play piano and returns to the apartment to confront Ripley. Ripley attacks Freddie and kills him by hitting him over the head with a heavy statue. He carries the body to Freddie's car and drives out to the woods where he leaves Freddie's body on the ground and abandons the car.
Freddie's corpse is quickly discovered, and Ripley's life becomes a cat-and-mouse game. He must now avoid both the police and Dickie's friends. He escapes capture and clears his name by faking a suicide note allegedly from Dickie and addressed to him. He moves to Venice and rents an apartment in his own name. Although Dickie's father still trusts Ripley, he hires a private detective called Alvin McCarron to investigate his son's death. Marge, having always suspected that Ripley was involved in Dickie's death, confronts him after finding Dickie's rings in Ripley's bathroom. Ripley seems to be close to murdering Marge, but is interrupted by their mutual friend Peter Smith-Kingsley who enters the apartment using the key Ripley gave him. McCarron, after unearthing some unsavory details about Dickie's past, tells Ripley that he is dropping the investigation. McCarron will not be sharing his findings with the police and asks Ripley to do the same. In return Greenleaf intends to transfer a significant portion of Dickie's trust fund into Ripley's name. Marge is angry about this and accuses Ripley of involvement in Dickie's death before she is forcibly removed by Greenleaf and McCarron.
Ripley and Peter, now in a romantic relationship, go on a cruise together only to discover that Meredith Logue is also on board. Ripley realizes that he will not be able to prevent them from communicating and also realizes that Meredith will tell Peter he has been pretending to be Dickie. He cannot murder Meredith, as she is with her family so he strangles Peter to death, sobbing whilst he does so. He returns to his cabin where he sits alone.