In Scotland, King Fergus of Clan DunBroch presents his young daughter Merida with a bow for her birthday. While practicing, Merida encounters a will-o’-the-wisp. Soon afterwards, Mor’du, a giant demon bear, attacks the family. Merida escapes along with her mother Queen Elinor while Fergus fights off the bear at the cost of his left leg. Years later, Merida has become a free-spirited teenager and an older sister of identical triplets: Hamish, Hubert and Harris. Her mother informs her that Merida is to be betrothed to one of her father’s allied clans. Reminding Merida of a legend about a prince who ruined his own kingdom, Elinor warns her that failure to marry could harm DunBroch. Despite the warning, Merida is dissatisfied with the arrangement.
The clans arrive with their first-born sons to compete in Highland Games for Merida’s hand. Merida declares she is eligible to compete for her own hand as the first-born of Clan DunBroch, causing a falling out between Merida and Elinor. After cutting the family tapestry in anger, Merida flees into the woods. There, the will-o’-the-wisps lead her to the hut of an elderly witch posing as a wood carver. After some bargaining, the witch agrees to give Merida a spell to change her mother; in the form of a cake.
Merida returns to the castle and gives Elinor the cake, causing her mother to transform into a large bear. With the help of her brothers, Merida and Elinor return to the witch’s now deserted cottage where they discover that the spell will be permanent unless undone by the second sunrise. The witch leaves Merida a riddle, mentioning that she must “mend the bond torn by pride.” The two begin to reconcile their relationship while Merida observes that the spell is slowly becoming permanent, as Elinor often loses control and acts like a bear. After encountering the wisps again, the two follow them to ancient ruins and discover that Mor’du was once the prince in Elinor’s legend, who received the same spell from the witch. Merida theorizes that she can reverse the spell by repairing her family tapestry.
At the castle, the clans are on the verge of war, but the princess quells their fighting and declares that the children should be allowed to get married in their own time. Merida then sneaks into the tapestry room with Elinor, who is losing control of her human self. Fergus enters the bed chamber and is attacked by Elinor until she regains human consciousness and races out of the castle in desperation. Fergus gives chase. With the help of her brothers, who have transformed into cubs by eating the cake, Merida rides after her father while sewing up the tapestry. The clan members and Fergus capture Elinor, but Merida intervenes just before Mor’du attacks. Elinor kills Mor’du by luring him under a falling menhir, releasing the prince’s spirit.
Merida places the tapestry over Elinor, but nothing happens. After breaking down in tears and reconciling with her mother, Elinor is transformed back along with the triplets, and the family is reunited. A few days later, the clans depart for their respective lands and Merida and Elinor ride their horses together.
In a post-credits scene, the witch’s crow asks a castle guard to sign for a delivery of wooden carvings that Merida bought simultaneously with the spell.