Austrian composer. He arranged Mahler's Symphony No. 6 for piano four hands. In addition to works for solo piano, he composed eight operas, oratorios, symphonies, choral works, and more.

After studying at the Vienna Conservatory, he served as Kapellmeister at the Vienna Volksoper and the Court Opera. He was also involved in music as a conductor of German opera and a teacher at the German Academy of Music. Until his exile to the United States in 1938, he joined a group of composers with Mahler as honorary president, and taught counterpoint to Schoenberg. Zemlinsky's sister became Schoenberg's first wife.