Matthew Poncelet, portrayed by Sean Penn, has been languishing on death row at the Louisiana State Penitentiary for six agonizing years after being sentenced for the tragic murder of a teenage couple. He committed these heinous acts alongside Carl Vitello, who received a life sentence without the possibility of parole. As Poncelet's execution date looms ever closer, he reaches out to Sister Helen Prejean, played by Susan Sarandon, a nun with whom he has had ongoing correspondence. Poncelet’s letters suggest a divine encounter, claiming that Jesus visited him in his cell.
Motivated by his pleas, Sister Helen decides to visit him. However, she quickly finds that Poncelet exhibits arrogance and displays deeply sexist and racist attitudes, showing an utter lack of remorse for his actions. The prison's chaplain, Farlely, discourages Helen’s involvement, believing Poncelet to be guilty and merely attempting to manipulate her goodwill.
Poncelet vehemently protests his innocence, insisting that it was Vitello who carried out the murders and that he was merely following orders under the influence of substances. He shares with Sister Helen a picture of his baby daughter, whom he has only met once in the past six years. He brags about having educated himself law and begins to formulate a motion for an appeal, seeking assistance from Helen to file it through legal channels.
Ultimately, Poncelet stands convicted of the kidnapping, sexual assault, and murder of Walter Delacroix and Hope Percy. This system of justice presents a staggering contrast: while Vitello received a lighter sentence, Poncelet faces the death penalty, carried out by the state’s newly implemented lethal injection protocol.
Determined to save him, Sister Helen secures the help of attorney Hilton Barber, who agrees to represent Poncelet pro bono. Hilton prepares Poncelet for the pardon board hearing, advising that if he can demonstrate his humanity, it might sway the board's decision. He emphasizes the importance of having Poncelet's mother, Lucille, and his brother, Craig, present during the hearing.
During the hearings, Hilton argues that Poncelet lacked the means to hire a competent attorney and was provided with an inexperienced public defender. The prosecution paints a grim picture, citing the suffering of the victims' families. After a swift jury deliberation, Poncelet is confirmed guilty numerous times—the board ultimately refuses clemency, scheduling the execution one week later.
As Helen continues her visits, she forges a complex relationship with Poncelet, while also connecting with the families of the victims who feel that Helen is betraying them by assisting a convicted murderer. The grieving families yearn for “absolute justice,” which they equate with Poncelet's execution. Faced with outrage from her own community, Sister Helen perseveres, trying to reason with Poncelet about the pain he has caused.
As the day of execution approaches, Poncelet requests that Sister Helen serve as his spiritual adviser. Amidst many discussions, both reveal personal memories and tragedies, including the heart-wrenching stories of how Hope was a week away from joining the Air Force when her life was brutally cut short. The contrasting emotions captured in Helen’s meetings with the victims' families highlight the enormous toll of crime and retribution.
Despite Poncelet’s continued arrogant posturing in interviews, he begins to see the weight of the losses inflicted. However, Helen is left infuriated by his flippant remarks glorifying violence and hate as he tries to dismiss their shared humanity. In the weeks preceding his execution, Helen embraces her role in helping Poncelet seek redemption through empathy and truth, encouraging him to look beyond his prejudices.
Ultimately, as Poncelet is moved to an isolated facility in preparation for execution, Sister Helen is able to spend lengthy sessions with him. She witnesses firsthand the final moments of his life, meeting those involved in the execution process and urging him to read the Bible, emphasizing that personal responsibility is key to redemption.
The night before his execution, Poncelet finally confesses the full extent of his crimes to Sister Helen, revealing that it was he who committed the acts of violence. As he faces his fate, he appeals for forgiveness from the victims’ families, voicing a desire that his death may bring them peace.
Poncelet meets his end by lethal injection, leading to a poignant burial attended reluctantly by the victims' families. Despite their personal strife, fragments of healing spark as the murdered boy's father finds himself praying alongside Sister Helen, hinting at the beginning of reconciliation amidst deep-seated anguish.
