The Austrian conductor and composer who promoted contemporary music in opera and concert.
Raised in Argentina, he first worked in Vienna and was Generalmusikdirektor (GMD) of the Royal Swedish Opera. He conducted notable world premieres such as György Ligeti's Requièm, Karlheinz Stockhausen's Carré, and Bernd Alois Zimmermann's opera Die Soldaten and his Requiem für einen jungen Dichter. He directed the Frankfurt Opera from 1977 to 1987, installing more contemporary operas, winning stage directors such as Hans Neuenfels and Ruth Berghaus, and reviving operas such as Schreker's Die Gezeichneten. During his era, the company became one of the leading operas.
Gielen was also principal conductor of the Belgian National Orchestra (1969–1973), the Cincinnati Symphony Orchestra (1980–1986) and the Southwest German Radio Symphony Orchestra (1986–1999). As a composer, he worked in the tradition of the Second Viennese School, often setting modern literature to music. His works were premiered with performers such as Joan Carroll, Siegfried Palm, Aloys Kontarsky and the LaSalle Quartet.