Rich and beautiful, Cordelia led her clique at Sunnydale High and enjoyed ridiculing those she saw as inferior. She first appears in "Welcome to the Hellmouth," sharing a textbook with Buffy Summers on her first day at the school and showing her to the library. Cordelia soon reveals herself to be a mean, popular cheerleader as she mocks Willow Rosenberg ("Good to know you've seen the softer side of Sears!"), much to Buffy's horror. That night, Buffy mistakes her for a vampire and almost impales her with a stake. Cordelia turns on Buffy and makes sure Buffy becomes a social outcast at the school.

Cordelia keeps finding herself in life-threatening situations in the first season, but often comes out untouched — she is almost killed by The Master's vessel, blinded by witchcraft, and targeted by a psychotic girl she helped snub into invisibility. Cordelia is elected May Queen in her sophomore year.

Cordelia grows to accept the existence of dark forces in Sunnydale and becomes a full-fledged member of the Scooby Gang. A corresponding fall in her social status reaches a low with her publicized romance with Xander Harris. It ends in Season Three when she finds him kissing Willow.

Cordelia struggles to revive her popularity when her father's "little mistake on his taxes...for the last twelve years" costs her family everything, including their house and her car, cell phone, and wardrobe. She takes a job at an expensive local boutique, April Fools, to pay for a prom dress on layaway. Cordelia does not earn enough in time, but Xander finds out and pays it off for her. Her brief, mutual infatuation with Wesley Wyndam-Pryce ends with two bad kisses before graduation.

After Cordelia left Sunnydale and went to Los Angeles, she failed as an actress. She then became a member of Angel's team and received visions to help him combat Wolfram and Hart and the usual villains.