The German conductor, Micael (Andreas) Gielen, is the son of the theatrical director Joseph Gielen. He studied under Erwin Leuchter in Buenos Aires (1942-1949), then under Josef Polnauer in Vienna (1950-1953).
An excellent pianist, Micael Gielen gave his debut in 1949 in Buenos Aires and played the complete piano works of Arnold Schoenberg in concert cycles. He became a répétiteur at the Teatro Colón, then he went to the Vienna Opera as a répétiteur (1950-1952) and conductor (1952-1960). From 1960 to 1965, Gielen was the principal conductor of the Stockholm Opera. In 1965 he conducted the first performance of one of the major operas of the 20th century in Cologne, Die Soldaten by Bernd Alois Zimmermann. From 1969 to 1972 he was the principal conductor of the Belgian National Orchestra, and from 1969 he was a permanent guest of the South German Radio Symphony Orchestra. From 1972 to 1975 he was the director of the Dutch National Opera. From 1977 to 1987 he was the chief musical director in Frankfurt, and in the same period from 1980 to 1986 he was the Musical Director of the Cincinnati Symphony Orchestra. In 1979 he also became the principal guest conductor of the BBC Symphony Orchestra, London. In 1986 he took on the directorship of the SWR Sinfonieorchester Baden-Baden & Freiburg (initially until 1999).
Micael Gielen taught orchestral conducting at the Salzburg Mozarteum until he became an emeritus professor in 1995.
Michael Gielen was a particularly keen proponent of the music of his contemporaries, and his first performances included Dramatic scenes from Orpheus by Hans Werner Henze (1982), D'un opéra de voyage (1967) by Betsy Jolas, Requiem (1965) and Ramifications (1st version, 1969) by György Ligeti, Zwei Stücke (1978) by Detlev Müller-Siemens, L'Effacement du prince Igor (1971) by Henri Pousseur, Carré and Mixtur (1965) by Karlheinz Stockhausen, Symphonic scene (1961) and Namo (1971) by Isang Yun, Die Soldaten (1965) and Requiem für einen jungen Dichter (1969) by Bernd Alois Zimmermann. A tour with this work in 1995 took him through Austria, Britain, France and Germany. His own compositions often followed on from the Second Vienna School.