After studies in piano and composition in Tokyo, he came to Berlin and Freiburg. In 1980, he participated in the Darmstadt Summer Courses for New Music. From 1990, he was a regular guest of the festival as a tutor.
From 1989 to 1998, the composer was the artistic director of the Akiyoshidai International Contemporary Music Seminar and Festival in Yamagushi which he had co-founded. Since 2001, he has additionally been the artistic director of the Japanese Takefu International Music Festival in Fukuj. He was appointed as permanent guest professor at the Tokyo College of Music in 2004.

Hosokawa’s compositions include orchestral works, solo concertos, chamber music and film music alongside works for traditional Japanese instruments. Influences from both Western music - from Schubert to Webern - and the culture of traditional Japanese music can be recognised in his compositions. Hosokawa considers the compositional process to be instinctively associated with the concepts of Zen Buddhism and its symbolic interpretation of nature.
Hosokawa has received numerous awards and prizes: Among them the first prize in the composition competition for the 100th anniversary of the Berliner Philharmoniker (1982), the Arion Music Prize (1984), the Kyoto Music Prize (1988) and the Rheingau Music Prize (1998). From 1998 to 2007 he was Composer in Residence at the Tokyo Symphony Orchestra. Hosokawa was appointed member of the Akademie der Künste in Berlin in 2001. In 2006/07 and 2008/09, he undertook a period of research at the Institute for Advanced Study [Wissenschaftskolleg] in Berlin.
He was Composer in Residence at the Biennale di Venezia (1995, 2001), the Tokyo Symphony Orchestra (1998-2007), the International Music Festival of Lucerne (2000), musica viva in Munich (2001), and others. He was Artistic Director of the Suntory Hall International Program for Music Composition from 2012-2015.