In 1968, as an audience of inmates at Folsom State Prison cheer for Johnny Cash, he waits backstage near a table saw, reminding him of his early life.
The film flashes back to 1944. Then-12-year-old JR (his name at birth was initials only) grows up on a cotton farm in Dyess, Arkansas with his brother Jack, father Ray, and mother Carrie. Ray is stern and strict with his sons but takes pride in Jack, who wants to be a preacher when he grows up.
Jack is killed in a sawmill accident while JR is out fishing. An embittered Ray blames JR for Jack’s death, saying that the Devil “took the wrong son.”
Six years later, now-adult JR has enlisted in the Air Force and prepares to leave home for duty in West Germany. His family says their goodbyes, except for Ray who barely acknowledges him. He purchases a guitar while on leave in 1952 and finds solace in writing songs and calling his girlfriend Vivian. One of the songs he develops is “Folsom Prison Blues”, inspired by a film that’s shown to the airmen.
Cash returns to the United States after his discharge and marries his girlfriend, Vivian Liberto. They move to Memphis, Tennessee, where he works as a door-to-door salesman to support his growing family. Vivian is frustrated by their poverty and urges him to work for her father, but he still dreams of a career in music. He walks past the Sun Records recording studio and is inspired to organize a band. Cash and his two bandmates auditions for Sam Phillips, the owner of Sun Records, but he is unimpressed by the gospel music they play. He asks Cash if he would play that song if he was hit by a truck and had time to play just one song before dying. Cash plays “Folsom Prison Blues”, and Phillips signs them. The band begins touring as “Johnny Cash and the Tennessee Two.”
The band plays a show in Louisiana alongside fellow rising stars Elvis Presley, Carl Perkins and Jerry Lee Lewis. Johnny meets June Carter on this tour and begins to fall in love with her. They become friends, but June gently rebuffs his attempts to woo her, reminding him that he’s married. Johnny’s fame grows and he begins to abuse drugs and alcohol.
Vivian is angry about his absences and seems to distrust his female fans and June. She objects when Johnny decides to handle his own bookings and persuades June to join the tour with him. The tour is a success, but backstage, Vivian becomes critical of June’s influence.
Johnny and June give a performance in Las Vegas and give in to their romance and sleep together. The next morning, June notices Johnny taking pills and has doubts about her choices. Hurt and angry about June’s apparent rejection, Johnny behaves erratically at that evening’s concert and passes out on stage. June disposes of Johnny’s drugs and begins to write “Ring of Fire” about her forbidden love for him and the pain of watching his descent into addiction.
Returning to California, Johnny travels to Mexico to purchase more drugs and is arrested. Vivian is fed up with his substance abuse, absences from home and her certainty that he’s unfaithful to her. Their marriage disintegrates and Vivian takes their children and leaves him. They divorce and he moves to Nashville in 1966.
Intent on reconciling with June, Johnny purchases a large house near a lake in Hendersonville. He invites his parents and the extended Carter family for Thanksgiving. Ray and an intoxicated Johnny get into a bitter argument during the meal. June’s mother Maybelle encourages her daughter to help him. He goes into amphetamine withdrawal and wakes up with June at his bedside. She says they have been given a second chance. Johnny suffers through cold-turkey detox and kicks his habit. They begin a tentative relationship, although June continues to refuse his marriage proposals.
Johnny discovers that most of his fan mail is from prisoners. He goes to a meeting proposes at Columbia Records and informs the skeptical executives that he will record a live performance album live inside Folsom Prison. The concert is a success.
Johnny embarks on a tour with June and his band. He performs “Ring of Fire” on stage. After that song, Cash invites June to a duet and stops in the middle, saying he cannot sing “Jackson” anymore unless June agrees to marry him. June accepts and they share a passionate embrace on stage.
Johnny, June, their children and extended family visit at his Hendersonville house. He and his father reconcile their relationship. A postscript tells viewers that they play and record music, tour the world for the following three decades. They have a son, John Carter Cash, together, and Johnny and June pass away within months of each other.