Catherine Ballou (Jane Fonda), an aspiring schoolteacher, is travelling by train to Wolf City, Wyoming, to visit her rancher father, Frankie Ballou (John Marley).
En route she unwittingly helps accused cattle rustler Clay Boone (Michael Callan) elude his captor, the sheriff, when Boone’s Uncle Jed (Dwayne Hickman), a drunkard disguised as a preacher, distracts the lawman.
She reaches the ranch to find that the Wolf City Development Corporation is trying to take away the ranch from her father, whose only defender is an educated Indian, Jackson Two-Bears (Tom Nardini).
Clay and Jed appear and reluctantly offer to help Catherine. She also wires legendary gunfighter Kid Shelleen (Lee Marvin) to come and help protect her father from fast-drawing Tim Strawn, alias Silvernose (he had his nose bitten off in a fight and replaced with a silver one), the hired killer who is threatening Frankie (also played by Lee Marvin).
Shelleen arrives but turns out to be a drunken stumblebum who is literally unable to hit the side of a barn when he shoots and whose pants fall down when he draws his gun.
Strawn kills Frankie, but the townspeople refuse to bring him to justice, and Catherine becomes a revenge-seeking outlaw known as Cat Ballou.
She and her four associates rob a train carrying the Wolf City payroll, and Shelleen, inspired by his love for Cat (unrequited because she loves Clay), shapes up and kills Strawn. Later he casually admits that Strawn was his brother.
Cat poses as a prostitute and confronts town boss Sir Harry Percival, owner of the Wolf City Development Corporation. A struggle ensues, Harry is killed and Cat is sentenced to be hanged on the gallows.
Just after the noose is placed around her neck, Uncle Jed (again as a fake preacher) cuts the rope as she falls through the trapdoor. Her gang then spirits her away in a daring rescue.
Cat (Catherine) Ballou
Kid Shelleen/Tim Strawn
Prof. Sam the Shade
Nat King Cole
The Sunrise Kid