During World War II, he was conscripted into the army, but on his first day, he injured his hand while learning how a gun worked and spent time in a military hospital.

Berio made a living at this time by accompanying singing classes, and it was in doing this that he met the American mezzo-soprano Cathy Berberian, whom he married shortly after graduating (they divorced in 1964).

He later attended the Internationale Ferienkurse für Neue Musik at Darmstadt, where he met Pierre Boulez, Karlheinz Stockhausen, György Ligeti and Mauricio Kagel.

In 1960, Berio returned to Tanglewood, this time as Composer in Residence, and in 1962, on an invitation from Darius Milhaud, took a teaching post at Mills College in Oakland, California.

His students included Louis Andriessen, Noah Creshevsky, Steven Gellman, Dina Koston, Steve Reich, Luca Francesconi, Giulio Castagnoli, Flavio Emilio Scogna, William Schimmel and Phil Lesh of the Grateful Dead.

[2] All this time, Berio had been steadily composing and building a reputation, winning the Prix Italia in 1966 for Laborintus II, a work for voices, instruments and tape with text by Edoardo Sanguineti that was commissioned by the French Television to celebrate the 700th anniversary of Dante Alighieri’s birth.

He gave a two-hour seminar at a summer school in the United States analyzing Beethoven's 7th Symphony, demonstrating that it was a work of radical genius.

The next day he gave another two-hour seminar, with a completely straight face, showing why it was hopelessly flawed and a creative dead-end.

[8] A later work, Visage (1961) sees Berio creating a wordless emotional language by cutting up and rearranging a recording of Cathy Berberian's voice; therefore the composition is based on the symbolic and representative charge of gestures and voice inflections, "from inarticulate sounds to syllables, from laughter to tears and singing, from aphasia to inflection patterns from specific languages: English and Italian, Hebrew and the Neapolitan dialect".

The work is one of a number of collaborations with the poet Edoardo Sanguineti, who for this piece provided a text full of quotations from sources including the Bible, T. S. Eliot and Karl Marx.

The work extends over roughly an hour, and explores a number of themes within a framework of folk music from a variety of regions: Chile, North America, Africa.

A line repeated often is "come and see the blood on the streets", a reference to a poem by Pablo Neruda, written in the context of the outbreak of the civil war in Spain.

Along with eleven other composers, (Conrad Beck, Pierre Boulez, Benjamin Britten, Henri Dutilleux, Wolfgang Fortner, Alberto Ginastera, Cristóbal Halffter, Hans Werner Henze, Heinz Holliger, Klaus Huber and Witold Lutosławski), Berio was asked by the cellist Mstislav Rostropovich to celebrate the Swiss conductor Paul Sacher's 70th birthday by composing a solo cello piece using the letters of Sacher's name (eS, A, C, H, E, Re).

Music Les mots sont allés has been performed since by cellists Siegfried Palm, Jean-Michelle Fonteneau, and Alexander Ezerman among others.

He also wrote an ending for Giacomo Puccini's opera Turandot (premiered in Las Palmas on 24 January 2002[12] and in the same year in Los Angeles, Amsterdam and Salzburg) and in Rendering (1989) took the few sketches Franz Schubert made for his Symphony No.

In "Two Interviews", Berio mused about what a college course in transcription would look like, looking not only at Franz Liszt, Ferruccio Busoni, Igor Stravinsky, Johann Sebastian Bach, himself, and others, but to what extent composition is always self-transcription.

Among Berio's other compositions are Circles (1960), Sequenza III (1966), and Recital I (for Cathy) (1972), all written for Berberian, and a number of stage works, with Un re in ascolto, a collaboration with Italo Calvino, the best known.