In this remake of the 1960 film of the same name, the small town of Rose Creek is being terrorized by land baron Bartholomew Bogue (Peter Sarsgaard) and his men. The townsfolk meet in the church to discuss what they ought to to protect their land and families from Bogue. The man himself enters the church with some of his armed men and he steps up before everyone else. Bogue argues that there is little profit in the land that makes up Rose Creek, so he intends to return within three weeks to see that the town has turned up more profit. The men then fire their guns and burn the church down. As the people evacuate, Matthew Cullen (Matt Bomer) calls Bogue out and asks what kind of man he is to harm innocent people. Bogue responds by shooting Matthew dead in front of his wife Emma (Haley Bennett), leading to a number of other citizens being killed by Bogue's men in front of their families. Before leaving, Bogue orders his men to leave the bodies where they lay so that the townspeople can get a good look at them for the next few days.
In another town, warrant officer Sam Chisolm (Denzel Washington) rides his horse into town, earning many unwelcome looks from the people. Chisolm enters a saloon and asks the bartender (Chad Randall) about an outlaw that goes by the name of "Powder Dan". The other men in the saloon draw their weapons on Chisolm, but he is quick with his gun and gets all of the men without skipping a beat. He then shoots the bartender dead, knowing that this is Powder Dan. Chisolm orders the people to fetch the sheriff, and all of them run out of the place terrified, except for one man, a gambler named Josh Faraday (Chris Pratt).
After Chisolm proves he caught Powder Dan, Faraday is caught up by two brothers that feel he cheated them in a card game. The brothers bring Faraday outside of town to kill him. Faraday distracts them with a card trick, which ends with him shooting one of the brothers dead and shooting the other one in the ear.
As Chisolm rides away, he is approached by Emma and her associate Teddy Q (Luke Grimes). She explains the town's situation with Bogue and their desperation in finding someone who can help. Emma and Teddy give Chisolm all the money they have, and when she mentions Bogue's name, Chisolm agrees to help.
Chisolm, Emma, and Teddy ride by Faraday as he tries to pick up his horse from a stablemaster. Chisolm offers to pay for Faraday's horse in exchange for Faraday joining their cause. He agrees. Chisolm then instructs Faraday to travel to Volcano Springs to find a man by the name of Goodnight Robicheaux (Ethan Hawke).
Faraday and Teddy arrive at Volcano Springs to witness a gunfight between two men. The first man believes that the second, Billy Rocks (Byung-hun Lee), didn't fairly win, so he demands a legit gunfight. As they are set to fire, Billy instead grabs his hairpin and throws it into the other man's chest, killing him. Robicheaux goes around collecting every man's bet. One man refuses until he learns Robicheaux's name, and then pays double out of fear. Robicheaux has a reputation for being a notorious sharpshooter. Faraday and Teddy approach the two men as Robicheaux gets a shave to discuss them joining the team. The two agree after learning it's a paid job.
Chisolm and Emma come across a house with a dead man inside. They find Vasquez (Manuel Garcia-Rulfo), a Mexican outlaw who's been squatting in the house. Chisolm is aware of the bounty on Vasquez, but he offers the outlaw a chance to avoid being captured by Chisolm in exchange for joining the team. Vasquez complies.
After both parties reunite, they search for a tracker named Jack Horne (Vincent D'Onofrio). They speak to two outlaw brothers on Horne's whereabouts. One brother is struck in the chest with a hatchet, and the other is shot dead. Horne shows up and takes the hatchet. Chisolm asks him to join their team, but Horne walks away without a response.
On the road back to town, the group encounters a Comanche named Red Harvest (Martin Sensmeier). Chisolm, knowing a little Comanche, speaks to him and asks for his help. Red drops his kill on the ground and cuts out one of its organs to offer it to Chisolm. He reluctantly bites into the organ to prove his loyalty, so Red agrees to join. Horne then joins after tracking the group down.
The group returns to Rose Creek and confronts some of Bogue's men in the middle of town. One of the men, McCann (Cam Gigandet), calls upon one of the shooters standing on the roof of a building. Red already got to him, and he drops the man's body off the roof. The team (except Robicheaux) then start fighting against Bogue's men. Red fires his arrows, Horne chucks his hatchets, Billy stabs several men, and the rest fire their guns at the villains. Robicheaux is more hesitant in shooting, allowing McCann to get away on his horse. When the dust settles, Chisolm orders the Sheriff to run back to Bogue in Sacramento and tell him that Chisolm is waiting for him.
Since the ride between Rose Creek and Sacramento takes three days, Chisolm figures they have about a week until Bogue returns with his army. The seven round up the townsfolk with Emma's help to inspire them to fight for their town and their families.
The men begin to train the townsfolk in using weapons. Billy instructs them on using knives, while Faraday and Robicheaux teach them to shoot. The inexperienced citizens don't get it immediately, but they pick up and do better. Emma manages to be a better shot after having learned from her father as a child.
Bogue receives the message from the Sheriff, then Bogue kills the messenger, literally. He begins to concoct his plan of attack.
The seven bond together in town at night through a meal, drinks, and some laughter. This brings them closer to the townsfolk as well, giving them more of a personal reason to fight. However, The seven and the townsfolk prepare for the arrival of Bogue and his army. Traps are laid out and people are at their stations.
Robicheaux becomes distressed over the thought of more killing, as he is haunted by the lives he's taken over the years. He tells Chisolm he wants no part of this and he decides to ride away into the night before the battle. Emma offers to take Robicheaux's place.
As Bogue's hired men charge in on their horses, Bogue and a handful of his men watch from a distance. The men ride by a line of pinwheels set up by Horne, who then detonates some explosives that throw the men off their horses. The people begin shooting at Bogue's men, while the men fire back. Vasquez shoots McCann dead right into a coffin. Bogue retaliates by having his men fire a Gatling gun into town, mowing down countless people. The women and children are evacuated to a safer area. Robicheaux returns to town and joins the fight with Billy atop a church steeple.
Bogue's own Comanche, Denali (Jonathan Joss), rides into town. Horne tries to fight him, but Denali takes him out with four arrows. Denali follows Emma into the saloon and tries to kill her when she shoots at him but has no bullets. Red shows up and fights Denali, ending with Red stabbing him and pushing him over a balcony.
Faraday, wounded in the gut, tells Chisolm the have to take out the Gatling Gun, and says Chisholm owes him cover, the two rush out, Faraday grabs a horse and begins a long sweeping charge toward The machine gun. Robicheaux and Billy provide covering fire from the Steeple. The gun crew is bemused as the lone attacker gets closer, they shoot at him.
The Gatling gun is fired a second time. Billy and Robicheaux are shot dead in the steeple. Faraday sustains multiple gunshot wounds before falling on his knees before a group of Bogue's men. He pulls out a cigar and puts it in his mouth. One of the men lights it for him before aiming the gun at Faraday. He slumps over, but then rises and shows a burning stick of dynamite. Faraday throws it at the men and it blows up in a huge explosion. Only Bogue and two henchmen are left.
Chisolm quickly takes out the two hired guns confronts Bogue right in front of the burnt-down church. They have a duel, with Chisolm shooting Bogue's gun out of his hand. He shoots Bogue in the leg as he tries running into the church. Chisolm offers Bogue a chance to pray. Chisolm starts strangling Bogue with his own ascot as he reminds Bogue that he and his men came into Chisolm's Kansas town, raping and murdering Chisolm's mother and sisters in the process. Chisholm has a neck scar, he had barely survived a lynching. Bogue reaches into his ankle holster to get a gun and shoot Chisolm, but he is shot dead by Emma.
Despite the massive destruction and untold lives lost, the surviving citizens are thankful to Chisolm, Vasquez, and Red. The people thank them all as they ride out of town.
The final scene shows the graves of Faraday, Robicheaux, Horne, and Billy. Emma's voice-over states that the people of Rose Creek will never forget the men that fought for something that wasn't theirs, and what they did was...MAGNIFICENT.