Carreras was born in Barcelona, Spain, and exhibited musical talent from a young age. At age eight, he also gave his first public performance, singing La Donna e Mobile on Spanish national radio. At eleven, he appeared at the Liceu as a boy soprano in the role of the narrator in Falla's El retablo de Maese Pedro and an urchin in the second act of La bohème. In his teens, Carreras studied at the Conservatori Superior de Música del Liceu. He made his debut at the Liceu as Flavio in Norma, coming to the attention of the famous soprano Montserrat Caballé, who sang the title role.