one of the most influential Italian composers of the 20th century. He is known for incorporating various avant-garde techniques into a highly personal style.

Petrassi was born to a family of modest means. He studied voice for some time at the Schola Cantorum di San Salvatore in Rome before he was forced to seek employment as an assistant at a music shop. There he attracted the attention of composer Alessandro Bustini, who offered Petrassi free piano lessons. Petrassi then studied composition with Bustini and organ with Fernando Germani at the Conservatory of Santa Cecilia in Rome, where he received diplomas in composition (1932) and organ (1933) and later taught harmony and composition (1934–36). In 1956 he taught composition classes at the Berkshire Music Center in Tanglewood, Massachusetts, and throughout his career he toured widely as a conductor. In 1959 he became a professor of composition at the Academy of Santa Cecilia, a position he held until 1974.

Petrassi composed in a variety of styles—his early music shows the influence of Alfredo Casella (Casella, Alfredo) and Paul Hindemith (Hindemith, Paul), while his later works were influenced by Igor Stravinsky (Stravinsky, Igor) and Arnold Schoenberg (Schoenberg, Arnold). Choral composition, as in Coro di morti (1940–41), the cantata Noche oscura (1950–51), and Orationes Christi (1974–75), played a major role in his development. In his later compositions he displayed an interest in 12-tone (12-tone music) procedures, and several of his eight concerti for orchestra (1931–72) are deeply atonal (atonality). Petrassi's compositions include orchestral works (Partita, 1932; Concerto No. 1, 1933–34), operas (Il cordovano, 1949; Morte dell'aria, 1950), ballets (La follia di Orlando, 1942–43; Ritratto di Don Chisciotte, 1945), chamber and keyboard music (Psalm IX for chorus, strings, brass, three pianos, and percussion, 1934–36; Kyrie, for chorus and strings, 1990), and songs.