The story takes place in a distant future, were humans are exiled on the edge of the galaxy. The Terrans have managed to maintain peace to their military strength, deceit and a powerful government. As their resources started to diminish, they began looking to other worlds, like the mysterious Protoss zone. The Terrans' world were invaded by the Zerg which are also involved in a war against the Protoss. The arrival of the Zerg, led by the Overmind and its Cerebrates, complicate the Terrans' civilization. As you enter the game, you become a colonial magistrate of the Terran Confederacy, joining forces with the marshal of Mar Sara, Jim Raynor. The player is then arrested by the Confederacy for destroying their property. Along with Raynor, you will be freed by the Sons of Korhal and join forces with the group. The Chau Sara colony is infested by the Zerg and quickly destroyed by the Protoss.
Tthe leader of the Sons of Korhal, Mengsk, lures Zergs to Confederate buildings and sacrifices his right-hand woman, the psychic Sarah Kerrigan, because she wouldn't give in to his plan. Raynor than quits the alliance with several soldiers and the player of the game. The Confederacy falls and Mengsk takes the Terran population under his control, naming himself king.
They player enters the second episode, where he becomes a Celebrate that controls Chrysalis, in one of them Kerrigan being captured. She is rebirth into the Swarm and adds power to the Zergs. In the meantime, Tassadar, a Protoss High Templar, distracts Kerrigan and one of his fellows Templars assassinates the Cerebrate Zasz. Zeratul and the Overmind connect for a short time but enough so that the Overmind learns the location of the Protoss home.In the third episode, the player will assume the role of Protoss fleet Executor, replacing the castway Tassadar. The player will have to fight the Zerg race on Aiur and capture Tassadar. Still, the player rebells and joins him, resulting in a war against the Protoss. Tassadar and the Dark Templar will show their faith to the Conclave and have Zeratul slay two Zerg Cerebrates.