Part One: The Departure (November 1957)

Madame Émery and her beautiful 17-year-old daughter Geneviève have a tiny, struggling umbrella boutique in the coastal town of Cherbourg in Normandy. Guy is a handsome young auto mechanic who lives with and cares for his sickly aunt and godmother Élise. Though Geneviève's mother disapproves, Guy and Geneviève are deeply in love; they plan to marry and name their first child Françoise. At the same time, Madeleine, a quiet young woman who looks after Guy's aunt, is secretly in love with Guy.

Guy is drafted to serve in the Algerian War. The night before he leaves, he and Geneviève pledge their undying love and make love, presumably for the first time.

Part Two: The Absence (January–April 1958)

Geneviève learns she is pregnant and writes to Guy, but his replies are sporadic. Her mother tells her to give up on Guy – he has forgotten her. Geneviève is courted by Roland Cassard, a kind, young, very wealthy Parisian jeweler; he wants to marry her despite her pregnancy. In one of the connections among Demy's trilogy of films, Roland had previously unsuccessfully wooed the title character in the earlier Lola (1961); now he relates a version of this story to Madame Émery. Madame Émery urges Geneviève to be sensible and choose a secure future with Roland. Roland announces that he will be going to Amsterdam for three months, and will wait for Geneviève's answer until his return. Geneviève marries Roland in a great cathedral, but she appears ambivalent about her decision.

Part Three: The Return (March 1959 – December 1963)

Returning injured from the war, Guy learns that Geneviève has married and left Cherbourg. He has a difficult time readjusting to civilian life. After an argument with his boss he quits his job, goes drinking in a seedy bar, and spends the night with a prostitute. When he returns to his apartment, Madeleine tells him that his aunt Élise has died.

Guy sees that Madeleine loves him, and he rebuilds his life with her help. Using the inheritance from his aunt he opens a new "American-style" gas station. Madeleine agrees to marry him, though she wonders whether he is merely on the rebound after losing Geneviève.

Four years later, on a snowy Christmas Eve, Guy and Madeleine are in the office of their gas station with their small son François. As Madeleine and François leave to visit Santa Claus, a car pulls in. The mink-clad driver is Geneviève, now wealthy and sophisticated. She has a young girl with her, their daughter Françoise.

Guy invites Geneviève into the warmth of the station's office, where they chat as a boy attends to Geneviève's car. Geneviève reveals this is her first time in Cherbourg since her marriage, and tells Guy that her mother died recently. When asked if he wants to meet his daughter, Guy declines.

Once the car is ready Geneviève and Guy finish their conversation. On her way out, Geneviève opens the door and pulls her collar tight against the cold before looking back at Guy one last time. She walks to her car and drives off. Madeleine returns with François, and Guy greets her with a kiss. As the camera pulls back, he frolics with his son in the snow, then picks him up and follows Madeleine inside as the red light of Genevieve's car flash in the foreground.