She spent her childhood in Riverrun, where she befriended her father's ward, Petyr Baelish. Although the ward fell in love with her and sought her hand, Catelyn never shared his feelings, seeing him as a little brother and nothing more. When she was twelve, it was announced that she was betrothed to Brandon Stark, heir of Winterfell, in what would strengthen the ties of friendship between the great houses.
Catelyn's betrothal to Brandon ended abruptly when he, along with his father, were killed by the Mad King, setting off Robert's Rebellion. During the Rebellion, Catelyn father's sought to continue the alliance, so she married Brandon's brother Eddard. She moved to Winterfell, where she and Eddard formed a strong and loving marriage.