Jackson “Jack” Maine, a famous country music singer privately battling an alcohol and drug addiction, plays a concert in California. His main support is Bobby, his manager and older half-brother. After the show, Jack visits a drag bar where he witnesses a performance by Ally, a waitress and singer-songwriter. Jack is amazed by her performance, and they spend the night talking to each other, where Ally discloses to him the troubles she has faced in pursuing a professional music career.
Jack invites Ally to his next show. Despite her initial refusal she attends and, with Jack’s encouragement, sings on stage with him. Jack invites Ally to go on tour with him, and they form a romantic relationship. In Arizona, Ally and Jack visit the ranch where Jack grew up and where his father is buried, only to discover that Bobby sold the land. Angered at his betrayal, Jack punches Bobby, who subsequently quits as his manager. Before doing so, Bobby reveals that he did inform Jack about the sale, but the latter was too inebriated to notice.
While on tour Ally meets Rez, a record producer who offers her a contract. Although visibly bothered, Jack still supports her decision. Rez refocuses Ally away from country music and towards pop. Jack misses one of Ally’s performances after he passes out drunk in public; he recovers at the home of his best friend George “Noodles” Stone, and later makes up with Ally. There he proposes to Ally with an impromptu ring made from a loop of guitar string, and they are married that same day at a church ministered by a relative of Noodles.
During Ally’s performance on Saturday Night Live, Bobby reconciles with Jack. Later, Jack and Ally fight after he drunkenly voices his disapproval of Ally’s new image and music, which is nominated for three Grammy Awards. At the Grammys, a visibly intoxicated Jack performs in a tribute to Roy Orbison, and Ally wins the Best New Artist award. When she goes up on stage to receive her award, Jack follows her, where he wets himself and passes out. Ally’s father Lorenzo berates Jack and Ally helps him sober up. Jack joins a rehabilitation program shortly thereafter.
Jack recovers in rehab for about two months, where he discloses to his counselor that he attempted suicide when he was 13 years old. He also mentions that he has tinnitus, which has been getting worse. He tearfully apologizes to Ally for his behavior, and returns home. Ally wishes to bring Jack to perform with her on the European leg of her tour; Rez refuses, prompting Ally to cancel the remainder of the tour so she can care for Jack.
Rez later confronts Jack, accusing him of holding Ally back. That evening, Ally lies to Jack, and tells him that her record label has cancelled her tour so she can focus on her second album. Jack promises that he will come to her concert that night, but after Ally leaves, he hangs himself in their garage.
Ally becomes inconsolable after Jack’s death. She is visited by Bobby, who explains Jack’s death was Jack’s own fault and not hers. Ally takes a song that Jack had written but never performed and sings it at a tribute concert, introducing herself as Ally Maine.