The son of a Jewish cantor studied at the Vienna Conservatory and was then in Prague student Zdeněk Nejedlý, Alois Haba and Josef Suk. From 1931 to 1938 he sat as a concert pianist for the New Music and stated, inter alia the quarter-tone works on his teacher Hába. In 1943 he came to the ghetto Theresienstadt, where he belonged to the group of composers. He was the only survivor from this group. In the concentration camp the composition to the Esther game listed there arose. Participants of the performance and the writer Milan Kuna later managed a reconstruction of the work. 1944 Reiner was spent in the Auschwitz concentration camp and from there to Dachau, where he was liberated.
After 1945 he worked as a freelance composer and served as Chairman of the Czech Music Fund and member of the Czech Society of Composers. Disgusted with the policies of the Communist Party of Czechoslovakia he joined after the suppression of the Prague Spring in 1970 from the Communist Party. In 1975, he set to music five poems Reiner Kunze.
Reiner left behind an extensive work to which, inter alia, two operas and a ballet, an overture and a suite, a violin and a piano concerto and a concerto for bass clarinet, numerous chamber music compositions, organ and piano pieces, choruses and songs, drama and film scores count. The realized by Miro Bernat Short Motyli tady nezijí ( Butterflies do not live here, 1958) with music by Reiner in 1959 awarded at the International Film Festival in Cannes Golden Palm.