Makoto Moroi, son of Saburo Moroi, graduated in 1952 from the Tokyo National University of Fine Arts and Music, where he had been a pupil of Ikenouchi; he also studied Gregorian chant privately with Paul Anouilh, and Renaissance and Baroque music with Eta Harich-Schneider. His career started brilliantly in 1953 when two of his works won international prizes : the Partita for flute (1952) won an ISCM prize; and the Composition no.1, his first orchestral work, received 7th prize at the Queen Elisabeth Competition, as well as the first prize in the Japanese radio music competition and the government sponsored Art Festival prize. He was awarded a second ISCM prize for the piano composition Alpha and Beta in 1955.

In May of that year he went to Europe to work in the Cologne electronic music studio. He returned to Tokyo after eight months and began work at the studio of Japanese radio: in autumn 1956 he completed there his first piece in the new medium, Seven Variations, composed with the assistance of Mayuzumi. The two composers were principal promoters of the summer festivals of new music (1957-63), given under the aegis of the Institute for 20th-Century Music.

In 1958 Makato Moroi won another ISCM prize for Kihaku na tenkai, a 12-note suite for soprano, singing in Sprechgesang style, and chamber orchestra. His other awards include an Otaka Prize (1963) and an Italia Prize (1965). In 1964 he met the shakuhachi player Chikuho Sakai and began to take a serious interest in the instrument; he wrote the virtuoso Five Pieces (1964) for him and gradually extended his interests to other Japanese instruments.

In 1968 he was appointed professor of composition at the Osaka Geijutsu Daigaku. He made several trips abroad in 1970-71 and was guest composer at the Brahmshaus, Baden-Baden, in 1971. From the late 1970s to the early 1990s he concentrated on writing essays and articles, on resuming his compositional activities he made particular use of the shakuhachi and the sanjugen, a modern 30-string koto. In 1994 he became the director of the newly-opened Saitama Arts Theatre.