Court records show Prejean sued California pageant executive director Keith Lewis and actress and former Miss USA Shanna Moakler in Los Angeles on Monday.
Prejean was fired in June by pageant officials, who cited missed scheduled appearances.
Prejean's attorney says that's not true and his client was ousted because of controversial remarks in April during the Miss USA pageant that marriage should be between a man and a woman.
Representatives for Lewis and Moakler said they had no public comment yet on the lawsuit.
Her lawsuit claims they told Prejean to stop mentioning God.