Jim Carrey as Joel Barish: A bookish introvert who enters a two-year relationship with Clementine Kruczynski. After their relationship ends, Clementine erases Joel from her memory, and he erases her from his mind in response. Charlie Kaufman depicted Joel with some of his autobiographical personality traits. Producers cast Carrey against type for his role as Joel, selecting him for his everyday appearance, as well as his comedic ability. According to Gondry, this was because "It's hard to be funny. It's far easier to take someone really funny and bring them down than do the opposite." To induce Carrey, an actor who typically portrayed high-energy roles, to portray a restrained character, Gondry would not allow him to improvise, a restriction he did not place on the other cast members (Carrey objected). Gondry also put Carrey off balance by giving misleading orders or by rolling the camera at the wrong time. Gondry believed this would make Carrey forget what he should do to be Joel, allowing him to go in character. In the 2017 Netflix documentary Jim & Andy, Carrey mentions a conversation with Gondry one year before shooting began for Eternal Sunshine of the Spotless Mind, shortly after Carrey had a breakup with an unspecified woman. Gondry saw that Carrey's emotional state at the time was "so beautiful, so broken" that he asked him to stay that way for one year to fit the character. In the documentary, Carrey commented, "That's how fucked up this business is." Nicolas Cage was Gondry's original choice to play Joel, but Cage was unavailable as he was in high demand from independent directors after his performance in Leaving Las Vegas.
Kate Winslet as Clementine Kruczynski: A spontaneous extrovert who, after breaking up with him after a two-year relationship, erases Joel Barish from her mind. Producers cast Winslet against type for her part as Clementine, as Winslet had previously featured heavily in period pieces. She received the role after she was the only actress to offer criticism on the script instead of pandering to the writers. After another actress won an Oscar, the studio attempted to make Gondry use her instead of Winslet for the role of Clementine, but Gondry threatened to walk from the project if that occurred. During filming, Gondry took Winslet to a separate room to coach her, and she wore wigs instead of dying her hair. Some commentators note how Clementine's character criticizes the Manic Pixie Dream Girl stock character several years before film critic Nathan Rabin coined the phrase. Most commentators discuss one particular example to demonstrate this criticism, wherein Clementine warns Joel she is flawed: "Too many guys think I'm a concept, or I complete them, or I'm gonna make them alive. But I'm just a fucked-up girl who's looking for my own peace of mind. Don't assign me yours." With her impulsiveness, emotional intensity (extreme mood changes), alcohol dependence, turbulent relationships, reckless behavior, and hasty idealization or devaluation of Joel, Clementine seems to exhibit traits of borderline personality disorder, although it is not clear whether Kaufman wrote her character with this specific diagnosis in mind. Gondry had earlier thought of casting Björk for the role of Clementine. She feared she would be emotionally affected and rejected the invitation after reading the script.
Kirsten Dunst as Mary Svevo: The receptionist for Lacuna who, while dating Stan Fink, has a crush on Howard Mierzwiak. While erasing Joel's memory, Howard's wife catches her kissing Howard. Howard's wife reveals Mary previously had a relationship with Howard, which Howard erased from her mind. She reacts to this information by quitting her job and mailing Lacuna's company records to its customers. In the script, Mary and Howard's relationship resulted in an unplanned pregnancy, leading to Howard pressuring Mary into an abortion, which Howard also erased from her memory.
Mark Ruffalo as Stan Fink: A technician for Lacuna who is in a relationship with Mary Svevo until the reveal of her previous relationship with Howard Mierzwiak. Ruffalo received the role of Stan after providing an "unexpected take on the role" to Gondry when he suggested Stan be a fan of the Clash and resemble Joe Strummer.[6]
Elijah Wood as Patrick Wertz: Patrick is a technician for Lacuna who enters a relationship with Clementine by imitating Joel. They break up when Joel and Clementine begin dating for the second time. Seth Rogen auditioned for the role.
Tom Wilkinson as Dr. Howard Mierzwiak: Howard runs Lacuna. Before the film's events, he had an affair with Mary, which ended with the relationship's erasure from her mind. Wilkinson reportedly did not enjoy the shooting of the film and clashed with Gondry.
Jane Adams as Carrie Eakin: Joel Barish's friend. She is in a troubled relationship with Rob Eakin.
David Cross as Rob Eakin: Joel Barish's friend. In a troubled relationship with Carrie Eakin.
Deirdre O'Connell as Hollis Mierzwiak: Howard Mierzwiak's wife
Thomas Jay Ryan as Frank: Joel Barish's neighbor
Debbon Ayer as Joel Barish's mother
Ellen Pompeo as Naomi, Joel Barish's girlfriend (deleted scene)