A young drifter finds success as a traveling preacher until his past catches up with him.

In the 1920s, Elmer Gantry entertains a group of fellow salesmen in a speakeasy with his ribald jokes and easy charm. When a Salvation Army worker enters, Gantry shocks and moves the crowd with an impromptu, impassioned sermon equating God with love. After collecting money from the patrons, Gantry takes a drunken barfly back to his hotel room. Despite his magnetism, Gantry remains penniless, and soon hops a train to avoid paying his hotel bill. There, a group of tramps steal his shoes and, to escape, he jumps off. Barefoot and filthy, Gantry enters an all-black church and soon wins over the crowd with his ardent singing. The minister, impressed with Gantry's knowledge of scripture, offers him dinner and work, and within days Gantry is back to his traveling sales job. Although he fails to sell any more of his defective household appliances, in one town Gantry is captivated by a poster advertising Sister Sharon Falconer, a visiting evangelist. After attending her prayer meeting, Gantry attempts to speak to the wildly popular preacher, and upon being politely turned away, manages to seduce one of her troupe, naïve Sister Rachel, into divulging information about Sharon's past appearances. Armed with this insider knowledge, Gantry follows the troupe onto a train for Lincoln, Nebraska and, after diverting Sharon's protective manager, William L. Morgan, Gantry sits next to Sharon and claims to know her. Although the exhausted Sharon is wary of Gantry, she appreciates his earthiness and charisma, and agrees to meet him the next day at her tent. Also following Sharon's troupe is cynical reporter Jim Lefferts, who respects Sharon's talent but remains unconvinced of her authenticity or effectiveness in converting people for longer than the few hours during which they remain in her thrall. Jim and Gantry are both present the next day to witness Sharon convince the Lincoln police that not only is the tent not a fire hazard, but that the city leaders need to oppose the attempts by local "whiskey slingers" to discredit her. Gantry, thoroughly impressed, tries to seduce Sharon into hiring him, but when he realizes that he cannot dupe her, informs her with only partially false sincerity that he wants to inspire sinners with the tale of his own moral redemption. Sharon allows him to speak, and she, Bill and Jim watch with awe as Gantry galvanizes the audience with his theatrical preaching about love, hellfire and deliverance. That night, Gantry attempts to kiss Sharon, prompting her to warn him that she is a true believer who will allow to him to remain only if he gives up drinking, smoking and carousing. Jim, who has overheard them, laughingly tells Gantry he could be "the most successful clown in the circus." To Bill's dismay, Jim's words prove true, as Gantry brings his sensationalist style to Sharon's ministry. As she preaches kindness and faith, he causes audience members to speak in tongues and beg forgiveness. Bill urges Sharon to fire Gantry, but she believes them a good pair, and is further convinced when they are invited to perform in Zenith, the biggest city in the Midwest. They meet with the Zenith church leaders, brought together by realtor George Babbitt. When many of the reverends express dismay at turning religion into a spectacle, Babbitt and Gantry counter that the churches must earn money to stay open, and Sharon's visits convert hundreds. Although the committee eventually agrees, many of the reverends remain concerned. The revival enters town with huge fanfare, orchestrated by Gantry, and soon the rapidly growing ministry is running like a factory. Sharon is exhausted by the press attention and frightened of the cynicism and sophistication of the urbanites who picket her tent, but Gantry convinces her that the picketing mobs are the most in need of her salvation. Sharon's solemn, quiet prayer wins over the crowd, and after the service, Gantry protects her from the now adoring fans. Jim, however, remains doubtful and embarks on a series of articles censuring the revival as a sham and revealing that neither Sharon nor Gantry has any credentials or must account for their earnings. Among the millions who read about the ministry is prostitute Lulu Bains, who as a teenager was thrown out of her house after Gantry seduced her by "ramming the fear of God into her." Although the public turns with vicious fervor against Sharon and Babbitt withdraws his financial support, Gantry, armed with proof that Babbitt's properties house illegal businesses, brings the businessman before Jim's editor, Eddington. Sharon is already there, arguing with Jim, who is criticizing her for claiming to know with certainty what God wants. Gantry steps in, and after forcing Jim to admit that he is an atheist, convinces Eddington that this revelation could harm the newspaper. In response, Eddington allows Gantry broadcast time on his radio station, paid for by Babbitt. Although Sharon is thrilled by Gantry's outrageous persuasiveness, when Gantry tries again to kiss her, she retorts that her only love is for God. Conciliating her gently, Gantry draws her into his arms. Within days, the city has embraced Gantry and Sharon as their spiritual leaders and Sharon, who is erecting a tabernacle nearby, is deeply in love with Gantry. One night, as a publicity stunt, he leads a group of reformers to raid a brothel, but when he recognizes Lulu among the arrested, Gantry convinces the police captain to release the girls. Soon after, Lulu asks Gantry to meet her at her hotel room. There, she and her pimp have arranged for a photographer to capture photos of her and Gantry embracing. When Gantry arrives, Lulu seduces him, but when he responds gently, she turns out the light so that no photograph can be taken. Gantry's love for Sharon prompts him to rebuff Lulu, who turns the light back on. The resulting photographs of them kissing goodbye are sent to Sharon, who agrees, with a broken heart, to pay Lulu for the negative. At the brothel, however, Lulu, consumed with spite, refuses the money and gives the pictures to the press. Public opinion immediately turns against Gantry, and at the next service, a riot erupts. Jim, who turned down the opportunity to publish the photos, is there, as well as Lulu, who is horrified to see what she has wrought. She runs from the church, followed by Gantry, who later finds her being beaten by her pimp for refusing Sharon's payment. Gantry rescues Lulu and holds her as she sobs. Later, Jim, who is surprised to realize that Gantry is truly religious, reveals that Lulu has announced in the press that she falsified the photographs. Although Gantry's reputation is restored, he disappears, to Sharon's dismay. Days later, as she prepares for her largest service ever, Gantry appears outside the tabernacle to ask her to run away with him. When she responds that she has been called by God, he realizes that she is consumed by her mission, and retreats sadly to the back of the church. Sharon's sermon inspires a deaf man to beg for her to heal him, and to the horror of both Gantry and Jim, Sharon, now believing herself a living conduit of God, lays her hands on the man and "cures" him. Just then, a man with a lit cigarette starts a fire. As the flames consume the church, a mesmerized Sharon entreats the hysterical crowd to stay and trust God. Gantry tries to rescue her but she breaks away and runs into the flames, her church collapsing around her. By the morning, Jim and Gantry sit among the wreckage. The reverential crowd asks Gantry to forgive them, but he explains that Sharon still loves them, and leads them in a psalm. Although Bill offers Gantry control of the ministry, promising to rebuild, Gantry responds by quoting the Bible: "When I became a man, I put away childish things."