In 1879, the ruthless Bartholomew Bogue, a robber baron and gold mining magnate, takes control of the frontier town of Rose Creek with an army of mercenaries, compelling the townspeople into cheap labor for his mine. Angered by their defiance, Bogue retaliates by burning down their church and brutally executing several residents, including farmer Matthew Cullen.
In a quest for justice, Matthew's widow Emma and her friend Teddy set off to find warriors who can help them reclaim their town. Their journey leads them to recruit Sam Chisholm, a renowned U.S. Marshal, who is keenly interested in confronting Bogue. Alongside Chisholm, an eclectic team forms: the daring gambler and sharpshooter Joshua Faraday, the pardon-seeking outlaw Vasquez, the seasoned Confederate marksman Goodnight Robicheaux, his accomplice, the skilled assassin Billy Rocks, and the legendary mountain man Jack Horne. They also enlist a Comanche warrior named Red Harvest.
Upon their arrival in Rose Creek, the group swiftly eliminates twenty-two of Bogue's private detectives. Chisholm captures the corrupt sheriff, Mr. Harp, sending him away under the pretense of challenging Bogue. He warns the frightened residents they have just seven days before Bogue's forces return. While some flee, the majority stand united to protect their home. The Seven free the men enslaved in the mines, commandeer explosives, and dedicate the week to fortifying the town and training the citizens for the impending conflict. Meanwhile, Bogue executes Harp and commands his Comanche enforcer Denali and lieutenant McCann to gather reinforcements. Haunted by his past in the Civil War, Robicheaux opts to leave but is replaced by Emma, who volunteers herself to fight.
On the dawn of the attack, Bogue's forces storm Rose Creek. The defenders utilize traps and ambushes, inflicting heavy casualties on the enemy. Faraday suffers a wound at the hands of McCann, who is subsequently slain by Vasquez. As the battle intensifies, Robicheaux returns, alerting everyone to an incoming Gatling gun. The streets become a chaotic battlefield, where many townspeople and mercenaries fall due to the relentless fire from the gun. In a desperate bid for survival, the Seven retreat to the charred remains of the church for one last stand.
Horne bravely shields a wounded Teddy but is ultimately killed by Denali. Just as Denali prepares to execute Emma, an infuriated Red Harvest intervenes, avenging his fallen comrades. Robicheaux and Billy heroically sacrifice themselves to protect Faraday, who charges the hill with dynamite, obliterating the Gatling gun but losing his life in the process. Chisholm confronts the last of Bogue's mercenaries before disarming Bogue himself. As Bogue retreats to the church, Chisholm reveals a painful truth about his family being lynched by Bogue's hired ex-Confederates. In a final interaction, as Chisholm urges Bogue to repent, the despicable baron attempts to draw a hidden revolver, but Emma ensures justice is served by taking him down.
As the townspeople of Rose Creek begin to rebuild, they express their gratitude to Chisholm, Vasquez, and Red Harvest for their bravery as they ride away. Meanwhile, they honor the fallen—Faraday, Robicheaux, Billy, and Horne—by burying them near the town and commemorating their heroic deeds. In a poignant voice-over, Emma reflects on the valiant sacrifices made, remembering the men as "magnificent."
