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 continued his studies with Klaus Huber at the Staatlichen Hochschule für Musik in Freiburg.

In 1980, Hosokawa participated for the first time in the Internationale Ferienkurse für Neue Musik in Darmstadt. Since then, his works have been performed regularly 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, he became a member of Akademie der Künste, Berlin.

Hosokawa 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 (1990-2006), La Biennale di Venezia (1995, 2001), 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, 2007). At the Münchener Biennale in 1998, his first opera Vision of Lear, commissioned by the City of Munich for the festival, was premièred. In 2004, his second opera Hanjo, commissioned by the Festival d'Aix-en-Provence, was premièred at the Festival La Monnaie in Belgium, and achieved an overwhelming triumph.

In August 2005, Hosokawa's orchestral work Circulating Ocean, commissioned by the Salzburg Festival, was premièred by the Vienna Philharmonic under the baton of Valery Gergiev and received its U.K. Première in August 2006 at the BBC Proms and its German Première at Berliner Philharmonie. Hosokawa was awarded the 5th Roche commissions in August 2008, and the commissioned work will see its Première at Lucern in August 2010. In 2011 his new opera Matsukaze commissioned by La Monnaie (Stage Director: Sasha Waltz) and a new horn concerto, co-commissioned by Berliner Philharmoniker, the Barbican Centre London and Zaterdag Matinee Amsterdam will be premièred.

Since 2001, he has served as Music Director for the Takefu International Music Festival. He was Composer-in-residence with Deutsches Symphonie Orchester Berlin in the 2006/2007 season and with WDR Rundfunkchor Köln in the seasons 2006-2008. Since 2004, he has been a guest professor at Tokyo College of Music. In 2006/2007 and again in 2008/2009 he was invited as one of the Fellows by Wissenschaftskolleg zu Berlin.