An avowed Marxist and member of the Italian Communist Party, Henze has produced compositions honoring Ho Chi Minh and Che Guevara. The librettist of his requiem for Che Guevara, titled Das Floß der Medusa (The Raft of Medusa), was among several people arrested at the 1968 Hamburg premiere for placing a red flag on the stage. Henze spent a year teaching in Cuba, though he later became disillusioned with Castro. His music is extremely varied in style, having been influenced at various times by atonality, Stravinsky, Italian music, and jazz.
Henze had some successful performances at Darmstadt, including an immediate success in 1946 with a neo-baroque work for piano, flute and strings, that brought him to the attention of Schott’s the music publishers. He also took part in the famous Darmstadt New Music Summer School, a key vehicle for the propagation of avant-garde techniques. At the 1947 summer school, Henze turned his thoughts more thoroughly to serial technique, and it seemed for a while as if he might become a leader of young German composers in this idiom.
In his early years he worked with twelve-tone technique, for example in his First Symphony and Violin Concerto of 1947. Sadler’s Wells Ballet visited Hamburg in 1948, which inspired Henze to write a choreographic poem, Ballett-Variationen, which was completed in 1949. The first ballet he watched was Ashton’s Scènes de Ballet. He wrote a letter of appreciation to Ashton, introducing himself as a 22 year-old composer. The next time he wrote to Ashton he enclosed the score of his Ballett-Variationen, which he hoped Ashton might find of interest. His Ballett-Variationen was first performed in Düsseldorf in September 1949, and staged first in Wuppertal in 1958. In 1948 he became musical assistant at the Deutscher Theater in Konstanz, where his first opera Das Wundertheater (after Cervantes) was created.
In 1950 he became ballet conductor at the Hessian State Theatre in Wiesbaden, where he composed two operas for radio, his First Piano Concerto as well as his first stage work of real note, the jazz-influenced opera Boulevard Solitude, a modern recasting of the traditional Manon Lescaut story.
Henze's move to the mainland of Italy strongly influenced his musical style which became enfused with the colourful tradition of Italian vocal music. His Five Neapolitan Songs for the eminent baritone Dietrich Fischer-Dieskau were written soon after his arrival in Naples. A later sojourn in Greece provided the opportunity to complete a work intended for another leading singer of the day: Kammermusik (1958), dedicated to Benjamin Britten, included settings of Hölderlin for the tenor Peter Pears (as well as involving the guitarist Julian Bream).
In 1961, Henze moved to Rome, which also signalled a strong leaning towards music involving the voice. His style subsequently softened and became more lyrical. He was subsequently disowned by the Darmstadt purists as something of a lost cause who had betrayed modern trends, while Boulez and Stockhausen walked out of a performance of a Henze première in 1958.
From 1962 until 1967, Henze taught masterclasses in composition at the Mozarteum in Salzburg, and in 1967 became a visiting Professor at Dartmouth College in New Hampshire. One of his greatest successes was the première of the opera Die Bassariden at the Salzburg Festival.
In the following period, he greatly strengthened his political involvement which also influenced his musical work. For example, the première of his oratorio Das Floß der Medusa in Hamburg failed when his West Berlin collaborators refused to perform under a portrait of Che Guevara and a revolutionary flag which his librettist had placed upon the stage. His politics also greatly influenced his Sixth Symphony (1969), Second Violin Concerto (1971) and his piece for spoken word and chamber orchestra, El Cimarrón, based on a book by Cuban author Miguel Barnet about escaped black slaves during Cuba's colonial period.
In 1976, Henze founded the Cantiere Internazionale d´Arte in Montepulciano for the promotion of new music, where his children's opera Pollicino premiered in 1980. From 1980 until 1991 he led a class in composition in the Cologne Music School. In 1981 he founded the Mürztal Workshops in the Austrian region of Styria, the same region where he set up the Deutschlandsberg Youth Music Festival in 1984. Finally, in 1988, he founded the Munich Biennale, an "international festival for new music theatre", of which he was the artistic director.
His later works, while arguably less controversial, continued his political and social engagement. His Requiem (1990-93) comprised nine sacred concertos for piano, trumpet and chamber orchestra, and was written in memory of the musician Michael Vyner who died young. The choral Ninth Symphony (1997), - “dedicated to the heroes and martyrs of German anti-fascism” – to a libretto by Hans-Ulrich Treichel based on motifs from the novel The Seventh Cross by Anna Seghers is a defiant rejection of Nazi barbarism, with which Henze himself lived as a child and teenager. His most recent success was the 2003 premiere of the opera L'Upupa und der Triumph der Sohnesliebe (English: The Hoopoe and the Triumph of Filial Love) at the Salzburg Festival, text by Henze himself, based on a Syrian fairy tale.
In 1995 Henze received the Westphalian Music Prize, which has carried his name since 2001. On November 7, 2004 Henze received an honorary doctorate for 'musical science' from the Munich Conservatory and Theater School.