The play focuses on Don Rodrigue and Chimène. Rodrigue's father, Don Diègue, is the old upstart general of Kingdom of Castile and past his prime, whereas Chimène's father is the successful current general, Comte de Gormas. Rodrigue and Chimène love each other, but any chance of marriage is brutally disturbed when Chimène's father insults Rodrigue's father. Torn between his love for Chimène and his duty to avenge his father's honour, Rodrigue chooses the latter and faces the general in a duel in which Don Gormas is killed. Without denying her love, Chimène asks the King for Rodrigue's head.
When the Moors attack, Rodrigue gets the chance to redeem himself in the eye of the nation, and, more importantly, gets a chance to win back Chimène with honour still satisfied. His victories on the battlefield win him the renown of the people, the title of "the Cid", and the gratitude of the King.
Chimène then approaches the King to request that one of his knights duel with Rodrigue for her honor's sake, with the goal of bringing her Rodrigue's head. Chimène chooses Don Sanche as her champion; although she dislikes him, she agrees to marry whoever is the victor of the duel to the death. The King agrees to the duel unhappily (he does not want to risk losing Rodrigue).
Rodrigue speaks to Chimène privately, saying that he will not defend himself against what is symbolically "her" hand. She finally persuades him to do his best, because if he wins, they will marry.
After the duel, Don Sanche (Chimène's champion), carrying a bloody sword, comes to where she is waiting. Chimène assumes the worst without giving him the chance to speak. Going before the king, she finally feels free to confess her love for Rodrigue because she believes him to be dead. Don Sanche then explains that Rodrigue disarmed him and granted him mercy. After the duel, Rodrigue returns straight to the king, leaving Don Sanche to bring his sword to Chimène.
Although they love each other, Chimène and Rodrigue are reluctant to marry because of their history, but the king says that although it seemed impossible at first, circumstances have proven that they were meant to be together. Still, he realizes they need time to adapt. Chimène will set the date for the wedding, up to a year in advance. Meanwhile, Rodrigue, known as the Cid, will conduct a war against the Moors in their own territory.