Berganza studied at the Madrid Conservatory, under Lola Rodriguez Aragon, who herself studied with Elisabeth Schumann. She credits her teacher with the complete process of her development, from a raw talent to a polished artist; throughout her career, she continued to study with Aragon, developing interpretations or working out minor vocal problems. Berganza made her professional debut in 1956 at the Madrid Athenaeum in Schumann's song cycle Frauenliebe und -Leben, and made her operatic debut at the Aix-in-Provence Festival as Dorabella in Così fan tutte. She made her Glyndebourne debut in 1958 as Cherubino. In the same year, she made her U.S. debut in Dallas, singing the comprimario role of Neris in a production of Medea. The Medea was Maria Callas, and Berganza later declared that she never learned as much about musical drama and stage discipline as from Callas, who treated her "like a younger sister," even insisting that Berganza be allowed to portray Neris as a young woman close to Medea's own age, rather than an older, matronly figure, as was customary. Berganza made her Covent Garden debut as Rosina in 1960; throughout the 1960s and early 1970s she sang mostly Rossini and Mozart. She made her Met debut as Cherubino in 1967.
Berganza first sang Carmen in 1977, and described it later as a deeply liberating experience -- personally as well as musically. In preparing the role, she visited Seville to observe gypsy women, read the original novel by Prosper Merimee, and studied the score deeply. She developed her own perceptions of Carmen: she was a free spirit within a restrictive culture, but far from being a prostitute or a tramp, and even possessing a certain sweetness. While many critics applauded her presentation, others found it lacking in blood and guts -- too "ladylike." (Berganza countered this with her observation that, far from being the flamboyant, hand-on-the-hip, promiscuous creatures of popular thinking, real Spanish gypsy women in fact follow a fairly rigid standard of decorum.) She brought the same kind of original thinking to the role of Zerlina in Don Giovanni, and in the famous Joseph Losey film, she sang her as a fully mature and sensual young woman, rather than a simple and bedazzled girl.
Berganza was also a prominent recitalist, specializing in Spanish song. Among her recordings, her Rosina (one of the most beautiful on record), and her collection of Spanish songs on Claves are both outstanding.