Cersei is the only daughter and eldest child of Joanna Lannister and Lord Tywin Lannister. Tywin is the head of House Lannister, the richest man in the Seven Kingdoms and Lord Paramount of the Westerlands. The Westerlands are one of the constituent regions of the Seven Kingdoms and House Lannister is one of the Great Houses of the realm. Cersei is the elder twin of Ser Jaime Lannister and the elder sister of Tyrion Lannister. She was raised in privilege in the family seat of Casterly Rock.She is noted for her great beauty.

Cersei's mother died when she was four years old, after giving birth to her younger brother Tyrion. Like her father, Cersei has always blamed Tyrion for her mother's death and deeply resents that her mother died so that Tyrion would be brought into the world.

She installed her son Joffrey Baratheon on the Iron Throne under the false claim that he was a legitimate son from her marriage but he was actually the product of her incestuous relationship with her younger twin brother Ser Jaime Lannister.