Toshio Hosokawa was born on October 23, 1955 in Hiroshima. He went to West Berlin to study composition with Isang Yun at the Hochschule der Künste in 1976. From 1983 to 1986, he studied with Klaus Huber at the Staatlichen Hochschule für Musik in Freiburg.

In 1980, he participated for the first time in the Internationale Ferienkurse für Neue Musik in Darmstadt where his work was performed. Since then Hosokawa has presented his works in Europe and Japan gaining an international reputation and winning numerous awards and prizes including first prize in the Composition Competition on the occasion of the 100th Anniversary of the Berliner Philharmonisches Orchester (1982), Rheingau Musikpreis (1998), Duisburger Musikpreis (1998) and musica viva-Preises der ARD und BMW AG (2001). In 2001, Hosokawa became a member of Akademie der Künste, Berlin.

He has been invited to nearly all of the major contemporary music festivals in Europe as composer-in-residence, guest composer or lecturer, including the Internationale Ferienkurse für Neue Musik in Darmstadt (1990–), La Biennale di Venezia (1995, 2001), Münchener Biennale (1998), Internationale Sommerakademie der Hochschule “Mozarteum” Salzburg (1998), Internationale Musikfestwochen Luzern (2000), musica viva in Munich (2001), Klangspuren in Schwaz (2002), Musica nova Helsinki (2003), Centre Acanthes in Villeneuve-lez-Avignon (2003) and Warsaw Autumn (2005). At the Münchener Biennale in 1998, his first opera, Vision of Lear, commissioned by the City of Munich for the festival, was premièred and highly acclaimed as “a work inspired by the encounter of East and West which has opened up a new musical world.”

In 2004, his second opera Hanjo, commissioned by the Festival d’Aix-en-Provence, was premièred at the festival and achieved an overwhelming triumph. In August 2005, his orchestral work, Circulating Ocean, commissioned by the Salzburg Festival, was premièred by the Vienna Philharmonic under the baton of Valery Gergiev and received its UK première in August 2006 in BBC Proms. His Lotus under the moonlight for piano and orchestra, which was commissioned by NDR on the occasion of Mozart Year 2006 received its world première and repeat performances in regular concerts of the NDR Sinfonieorchester with the soloist Momo Kodama and the conductor Jun Märkl in April 2006. The work was also well-received when it was first performed in Japan by Momo Kodama and the Mito Chamber Orchestra conducted by Seiji Ozawa in December 2006. In January 2007, the German première of Circulating Ocean took place in Berlin by the Deutsches Symphonie Orchester Berlin under the baton of Kent Nagano.

Since 1998, Hosokawa has served as composer-in-residence at the Tokyo Symphony Orchestra. He is also composer-in-residence with the Deutsches Symphonie Orchester Berlin (2006/2007) and with the WDR Rundfunkchor, Köln (2006–2008). Since 2001, he has served as music director for the Takefu International Music Festival. In 2004, he was appointed a guest professor at Tokyo College of Music.

Hosokawa, who is resident in Berlin, has also been invited to be one of the 2006/2007 Fellows by the Wissenschaftskolleg zu Berlin.