Brittany Pierce (Heather Morrison) is beautiful but not bright. She is part of the popular crowd and member of the nationally known cheerleading team "The Cherrios" at McKinley High School. Her best friends and fellow Cherrios are Santana Lopez (Naya Rivera) and Quinn Fabrey (Dianna Agron). Though she lacks in intelligence, once forgetting her right from her left, she remains popular as a result of her promiscuity and her assertion that she has made out with "every boy and several girls" at school. When Kurt Hummel (Chris Colfer) tries to make his teammates and classmates believe that he is not a homosexual, Brittany approaches him and wants to make out with him because "a perfect record would mean a lot to her".
Brittany, Santana and Quinn are forced to become spies for The Cherrios coach Sue Sylvester (Jane Lynch) who wants to destroy the glee club because the team budget has been cut to support the addition of the group. The girls schedule an audition and are able to win over the glee club coach Mr. Schuester (Matthew Morrison) with a rendition of "I Say A Little Prayer For You". Mr. Schuester accepts the trio into the glee club and they begin reporting back to Coach Sylvester after each practice.
Brittany is most helpful in Coach Sylvester's plans by giving her the songs on the set list which the glee club is planning to sing at the upcoming Sectional competition. She did this without malice, as she was oblivious to why her coach would want the list. When Coach Sylvester passes that information on to the rival schools, they sing the songs that the McKinley High glee club had planned to perform. They are unable to recover and they lose the competition. Brittany feels badly and confesses that she was the one who leaked the set list to Sue. She decides that she will no longer be her coach's spy and makes the decision to participate in both the glee club and The Cherrios but in an honest and forthcoming way.
For the majority of the first season, Brittany performs backup vocals and dances during musical numbers. It is in the second season that she is really allowed to let her vocals shine. She was a major contributor to an episode that paid tribute to the music of Brittany Spears, in which she sang two solos and one duet with Santana.
Brittany's naïve one liners add to the comic nature of the show. Though she is at times completely oblivious to world around her, she is kind and sweet at heart, even going as far as befriending a classmate with Downs Syndrome and helping her become a Cheerio.
"I think my cat reads my diary."
"Did you know that dolphins are just gay sharks?"
"I've been here since first period. I have a cold. I took all my antibiotics at once and now I can't remember how to leave."
"It's not that, it's that most of us don't know how to bake. I find recipes confusing. "