In the picturesque coastal village of Cherbourg, Normandy, Madame Émery and her 17-year-old daughter Geneviève run a small umbrella shop, striving to make a living. Amidst their struggles, Guy, a devoted auto mechanic, prioritizes caring for his ailing aunt and godmother, Élise. Despite her mother's disapproval, Geneviève and Guy are completely smitten with each other and dream of a future together, even naming their first child Françoise. However, lurking in the shadows is Madeleine, a reserved young woman who looks after Guy's aunt while secretly harboring feelings for him.
As Guy prepares to face the Algerian War, he and Geneviève share an unforgettable passionate night, solidifying their love. Back in Cherbourg, Geneviève discovers she's expecting and reaches out to Guy, but his replies are infrequent. Her mother pressures her to move on, convinced that Guy has forgotten her. Shortly afterward, she catches the attention of Roland Cassard, a thoughtful jeweler from Paris, who promises her stability despite her pregnancy. Interestingly, Roland had previously shown interest in the title character from Demy's earlier film, Lola, and shares this tale with Madame Émery, encouraging Geneviève to prioritize a secure future over her passionate feelings.
Eventually, Geneviève ties the knot with Roland in an opulent cathedral, though her hesitance about the marriage is evident. Simultaneously, Guy returns from war, grappling with his traumatic experiences and struggling to adapt to life away from the battlefield. Following a fallout with his boss, he resigns and drowns his sorrows at a dingy bar, seeking solace with a prostitute. The next day, Madeleine brings him heart-wrenching news: his aunt Élise has died.
As Guy faces the repercussions of Geneviève's absence coupled with his internal conflicts, he starts to piece his life back together, aided by Madeleine’s support. With his inheritance, he opens a modern "American-style" gas station, signaling a new chapter. Although Madeleine agrees to marry him, she can’t help but wonder if his feelings are genuine or just a fallout from losing Geneviève.
On a chilly Christmas Eve, four years later, Guy and Madeleine—along with their adorable son François—find themselves cozily situated in their gas station. As Madeleine and François head to visit Santa Claus, a sleek sedan pulls up, revealing Geneviève, now radiating elegance in her mink coat. She is accompanied by Françoise, their lovely daughter.
When Geneviève steps out, Guy warmly invites her into his office, and they share a significant conversation as a diligent attendant services her car. Geneviève mentions this being her first visit back to Cherbourg since her marriage and sorrowfully informs him about her mother's recent passing. When asked if he wishes to meet his daughter, Guy calmly declines.
As their conversation winds down, Geneviève prepares to leave. She pauses in the cold, adjusting her collar against the chill, and throws one last lingering look at Guy before stepping into the night. With Françoise comfortably seated in her car, she drives off into the wintry landscape.
Meanwhile, Madeleine emerges from her visit to Santa Claus, joined by François, and is greeted with a loving kiss from Guy. After a playful snowball fight, Guy scoops up their son and follows Madeleine inside, where they joyfully bask in the warmth of their home.
