Ned Kelly begins his autobiography with a description of his father, John "Red" Kelly, an Irishman transported to Van Diemen's Land and eventually settling in the colony of Victoria, Australia. After marrying Ned's mother Ellen (née Quinn), the Kellys settle in Avenel, a rural area northeast of Melbourne. Red Kelly is shown to have numerous brushes with the colonial police forces, resulting in his imprisonment and death when his son Ned was twelve years of age.
After the rest of the family resettles in northeast Victoria under the Land Grant Act, Ned's mother attempts to provide for her children by running a shebeen and taking on a series of lovers, including the notorious bushranger Harry Power. Power agrees to take on the young Ned as an apprentice, and provides Ned with knowledge of the land, hideouts, and strategies for bushranging. Kelly eventually leaves Power and returns to his family's settlement, where he is shown making dogged attempts to live an honest lifestyle.
Kelly is arrested and sentenced to three years in prison for reception of a stolen horse (although Kelly claims that a friend, "Wild" Wright, knowingly sold him the stolen horse without Kelly's knowledge– Kelly later exacts revenge on Wright in a bare-knuckle boxing match). After two years of working as a sawmill hand, he is drawn back to bushranging when a herd of his horses is appropriated by a rival squatter. His descent back into crime is precipitated by a visit from a local police officer, Constable Alex Fitzpatrick. The policeman woos Ned's younger sister Kate, prompting Ned to reveal that Fitzpatrick has multiple mistresses in other towns and has no intention of marrying Kate. After his mother Ellen threatens the constable with violence, Fitzpatrick pulls his revolver on the family and Ned shoots him in the hand in self-defense. Although he dresses the wound and Fitzpatrick leaves while promising that no action will be taken, warrants for the arrest of Ned and his younger brother Dan are issued the next day.
Ned Kelly and his brother Dan hide out in the hills of northeast Victoria, eventually being joined by their friends Steve Hart and Joe Byrne (later becoming known as the Kelly Gang). Kelly's mother is eventually arrested along with her baby daughter and imprisoned in Melbourne as enticement for Kelly to give himself up. A detachment of four policemen is eventually sent to kill the quartet after efforts to arrest them prove unsuccessful; the Kelly Gang ambushes them at Stringybark Creek, where Ned kills three of the policemen. This adds to the growing folklore surrounding the Kelly Gang, which they fuel by robbing banks and giving parts of the money to the lower-class settlers in Victoria who help to shelter the gang.
During the gang's raids, Ned Kelly meets a young Irish girl named Mary Hearn, who already has a young son by Kelly's stepfather, George King. Kelly falls in love with Mary and makes plans to escape the colony with her after she becomes pregnant with his child. Crucially, it is Mary who motivates Kelly to begin writing the story of his life as a legacy for his future child, who she fears will never know its father. Following two successful bank robberies, Mary uses the money to emigrate to San Francisco with her son and Kelly's unborn daughter; Kelly remains behind, however, unwilling to leave Australia until his mother is released from jail.
The gang is eventually cornered by a large squad of dozens of policemen (versus just four in the Kelly Gang) in the town of Glenrowan where the gang has taken numerous hostages and constructed several suits of plate-steel armor for protection. One of the hostages is the crippled local schoolmaster, Thomas Curnow, who encourages Kelly to relate the story of his entire life after seeing samples of his writing. Curnow betrays the gang by warning the incoming police train that the gang has sabotaged the tracks, feeling that history will view him as a "hero". The policemen surround the town and engage in a furious shootout with the armor-clad gang, seriously wounding Ned Kelly and killing the other three members of the gang. Kelly's narrative stops abruptly just before the shootout itself; a secondary narrator, identified as "S.C", relates the tale of the gunfight and Kelly's death by hanging. Since Curnow is shown to have escaped Glenrowan with Kelly's manuscripts, it is assumed that this narrator is a relative of Curnow's. Kelly dies a hero to the people of northeastern Victoria, with the legend of his life left to grow over time.