In 1280, Edward I of England, known as "Longshanks", conquers Scotland following the death of the Scots' king, who left no heir. Young William Wallace witnesses Longshanks' execution of several Scottish nobles, then loses his father and brother when they resist the English. He is taken on by his paternal uncle, who educates him.
Years later, Longshanks grants his noblemen land and privileges in Scotland, including jus primae noctis, while his son and heir reluctantly marries Isabella of France. Meanwhile, a grown Wallace returns home and secretly marries his childhood friend Murron MacClannough. Wallace rescues Murron from being raped by English soldiers, but as he fights off the soldiers, Murron is captured and publicly executed. In retribution, Wallace and the locals overthrow the English garrison, beginning a rebellion. Longshanks orders his son to stop Wallace while he campaigns in France. Wallace defeats an English army at Stirling, then invades England and sacks York. He also connects with Robert the Bruce, a contender for the Scottish crown. Upon returning to England and confronting his son, Longshanks sends Isabella to negotiate with Wallace as a distraction from the arrival of Longshanks' forces. After meeting Wallace, Isabella becomes enamored with him. She warns him of Longshanks' plans, and Wallace implores the Scottish nobility to help him. Wallace faces Longshanks at Falkirk. During the battle, nobles Mornay and Lochlan withdraw, having been bribed by Longshanks, resulting in Wallace's army being overwhelmed. Wallace also discovers Robert the Bruce had joined Longshanks. After the battle, Robert vows to not be on the wrong side again.
Wallace kills Mornay and Lochlan for their betrayal and foils an assassination plot with Isabella's help, while Longshanks' health declines. At a meeting in Edinburgh, Wallace is captured. Learning of his father's responsibility, Robert disowns his father. In England, Wallace is tried for high treason and condemned to execution. After a final meeting with Wallace, Isabella tells Longshanks, who can no longer speak, that his bloodline will end upon his death as she is pregnant with Wallace's child and will ensure that Longshanks' son spends as short a time as possible as monarch before Wallace's child replaces him. At his execution, Wallace refuses to submit, even while being disemboweled. The magistrate encourages Wallace to seek mercy and be granted a quick death. Wallace instead shouts, "Freedom!", while Longshanks dies. Before being beheaded, Wallace sees a vision of Murron in the crowd.
In 1314, Robert, now Scotland's king, faces the English at Bannockburn, and implores his men to fight with him as they did with Wallace. Wallace's former comrade, Hamish, throws Wallace's sword to land point-down in the ground, then Robert leads the Scots to a final victory.
