Michael Gielen was among the best-known conductors in Europe, and was the leading European conductor of Central European avant-garde music. He was also a respected composer of complex, often twelve-tone, compositions.
Michael Andreas Gielen's father was the stage producer Josef Gielen and his uncle was the eminent Polish pianist Eduard Steuermann, who was Arnold Schoenberg's first important piano interpreter. The family moved to Buenos Aires in the 1930s, where Michael studied piano and composition with Erwin Leuchter. He debuted in Buenos Aires in 1949 as a pianist. During that year, he played all of Arnold Schoenberg's piano compositions. He also worked as a coach in the Teatro Colón Opera House.
In 1950 he moved to Vienna to study with Polnauer (1950-1953). While there he found a position as coach in the Vienna State Opera, and in 1954 became a resident conductor on its staff, remaining there until 1960. In that year he was appointed music director of the Royal Opera of Stockholm (1960-1965), then as a regular conductor of the Cologne Radio Symphony Orchestra (1965-1969) then chief conductor of the Belgian National Orchestra in Brussels (1968-1973), and was director of the Dutch National Opera (1972-1975).
From 1969 he was the permanent guest conductor of the South German Radio Symphony Orchestra. By this time he was closely associated with the latest modernist trends in European music, particularly in twelve-tone idioms. Among his most important premieres were the opera Die Soldaten by Bernd Alois Zimmerman (Cologne, 1965), György Ligeti's Requiem (1965), D'un opéra de voyage by Betsy Jolas, Carré and Mixture by Karlheinz Stockhausen, Namo by Isang Yun, and Zimmermann's Requiem für einen jungen Dichter. In the meantime he continued to compose, normally dense, complex music taking its point of departure from the serial music of the time.
From 1978 to 1981 he was principal guest conductor of the BBC Symphony Orchestra in London, and from 1977-1987 he was chief music director of the Opern- und Schauspielhaus Frankfurt. Coterminously, he was music director of the Cincinnati Orchestra (1980-1986), a period known for its challenging programming.
He received one of his most important posts, director of the South-West German Radio Symphony in Baden-Baden, which is one of the leading orchestras in the modern music world, in 1996. There he has focused on the entire repertory from Bach to contemporary music, giving incisive performances of the complete Beethoven and Mahler symphonies. In 1999 he relinquished the post of music director, and became permanent guest conductor of the orchestra. Gielen passed away in March 2019.