In 1880, Frank Ross, of Yell County, Arkansas, is murdered and robbed by his hired hand, Tom Chaney. Ross's young daughter, Mattie, travels to Fort Smith, where she hires aging U.S. Marshal Reuben "Rooster" J. Cogburn to apprehend Chaney. Mattie has heard that Cogburn has "true grit". Mattie earns the money to pay his fee by shrewdly horse trading. She gives Cogburn a payment to track and capture Chaney, who has taken up with outlaw "Lucky" Ned Pepper in Indian Territory (modern-day Oklahoma).
A young Texas Ranger, La Boeuf, is also pursuing Chaney and joins forces with Cogburn, despite Mattie's protest. The two try, unsuccessfully, to ditch Mattie.
After several days, the three discover horse thieves Emmett Quincy and Moon, who are waiting for Pepper at a remote dugout cabin. Cogburn captures and interrogates the two men. Moon's leg is injured and Cogburn uses the injury as leverage for information about Pepper. Quincy stabs Moon to prevent this, and Cogburn kills Quincy. Before Moon dies, he reveals Pepper and his gang are due at the cabin that night for fresh mounts.
Rooster and La Boeuf lay a trap. Upon arriving, Pepper is suspicious and draws La Boeuf's fire, who ruins their planned ambush by shooting and killing Pepper's horse. A firefight ensues, during which Cogburn and La Boeuf kill two of the gang, but Pepper and the rest of his men escape unharmed. Cogburn, La Boeuf, and Mattie make their way to McAlester's store with the dead bodies. Cogburn tries to persuade Mattie to stay at McAlester's.
The two lawmen and Mattie resume their pursuit. Fetching water one morning, Mattie finds herself face-to-face with Chaney. She shoots Chaney with her father's gun, injuring him, and then calling out to her partners. Pepper and his gang arrive first, capture Mattie and force Cogburn and La Boeuf to abandon the girl and ride away. Pepper leaves Mattie with Chaney, instructing him not to harm her.
Cogburn and La Bouf double back. La Boeuf finds Mattie and they watch from a high bluff as Cogburn confronts Pepper and his gang of three. Cogburn gives Pepper a choice between being killed now, or surrendering and being hanged in Fort Smith. Calling this "bold talk for a one-eyed fat man" (Cogburn wears an eye patch), Pepper enrages Cogburn, who charges the four outlaws, guns blazing. In the initial head-on charge, Cogburn hits Ned in the chest above the heart. Cogburn eventually kills the Parmalee brothers with "Dirty Bob" fleeing. In the fight, Ned shoots Rooster's horse, trapping Rooster's leg under him as he goes down. As a last act, the mortally wounded Pepper prepares to kill Rooster, until La Boeuf makes a long shot with his Sharps rifle and kills Ned.
As La Boeuf and Mattie return to Pepper's camp, Chaney comes out from behind a tree and strikes La Boeuf in the head with a rock, fracturing his skull and knocking him unconscious. Mattie is able to shoot Chaney and sends him over a cliff. Driven back by the recoil, she falls into a snake pit and is caught by a root. Cogburn appears, and great difficulty, descends into the pit on a rope to retrieve Mattie, who is bitten by a rattlesnake.
Cogburn is forced to leave La Boeuf behind as he and Mattie race to get help on Mattie's pony, which drops from exhaustion. Cogburn shots and kills the suffering pony.
Sometime later, Mattie's attorney, J. Noble Daggett, (John Fiedler) meets Cogburn in Fort Smith. On Mattie's behalf, Daggett pays Cogburn for his part in Chaney's capture, plus a bonus for saving her life. Cogburn offers to wager the money on a bet that Mattie will recover just fine, a bet Daggett declines.
In the epilogue, Mattie, her arm in a sling, is back at home recovering from her injuries. She promises Cogburn he will be buried next to her in the Ross family plot after his death. Cogburn accepts her offer and leaves, jumping over a fence on his new horse to disprove her good-natured jab that he was too old and fat to clear a four-rail fence.
John Wayne as Reuben J. "Rooster" Cogburn
Glen Campbell as La Boeuf
Kim Darby as Mattie Ross
Jeremy Slate as Emmett Quincy
Robert Duvall as Lucky Ned Pepper
Dennis Hopper as Moon
Alfred Ryder as Goudy
Strother Martin as Col. G. Stonehill
Jeff Corey as Tom Chaney
Ron Soble as Captain Boots Finch
John Fiedler as Lawyer Daggett
James Westerfield as Judge Parker
John Doucette as Sheriff
Donald Woods as Barlow
Edith Atwater as Mrs. Floyd
Carlos Rivas as Dirty Bob
Isabel Boniface as Mrs. Bagby
H. W. Gim as Chen Lee
Ginger Cat as General Sterling Price (uncredited)
John Pickard as Frank Ross
Elizabeth Harrower as Mrs. Ross
Ken Renard as Yarnell
Hank Worden as R. Ryan, the undertaker at Fort Smith
Jay Ripley as Harold Parmalee
Kenneth Becker as Farrell Parmalee
Wilford Brimley as Minor Role (uncredited)
Leo Alton as Boarding House Guest (uncredited)
Forrest Burns as Courtroom Spectator (uncredited)
Gene Coogan as Boarding House Guest (uncredited)
Myron Healey as Deputy at Prisoner Unloading (uncredited)
Boyd "Red" Morgan as Red (Ferryman) (uncredited)
James McEachin as Judge Parker's Bailiff (uncredited)
Dennis McMullen as Bailiff (uncredited)
Robin Morse as Bit Part (uncredited)
Stuart Randall as McAlester (uncredited)
Connie Sawyer as Talkative Woman at Hanging (uncredited)
Jeffrey Sayre as Courtroom Spectator (uncredited)
Jay Silverheels as Condemned Man at Hanging (uncredited)
Dean Smith as Minor Role (uncredited)
Vince St. Cyr as Gaspargoo (uncredited)
Max Wagner as Courtroom Spectator (uncredited)
Guy Wilkerson as the Hangman (uncredited)
Chalky Williams as Courtroom Spectator (uncredited)
Tom Gosnell as John Wayne stunt double (uncredited)
the first film adaptation of Charles Portis' 1968 novel of the same name