Reiner was born in Budapest in 1888. He graduated from the Budapest Academy of Music in 1908 where he studied with Bela Bartok. Various conducting and directing appointments followed in Budapest and in Dresden, including that of chief conductor of the Royal Opera House in Dresden for 1914-1922. An acquaintance of Richard Strauss, Reiner was influenced by conductor Arthur Nikisch and Hungarian composer Leo Weiner. In 1922 Reiner left Europe to become the appointed director of the Cincinnati Symphony Orchestra, a post he held until 1930. In 1928 he became an American citizen. He married his second wife, Cincinnati actress Carlotta Irwin, in 1930.

From 1931-1941 Reiner served as head of the orchestra and opera departments at the Curtis Institute of Music, where Leonard Bernstein was his student. He supervised activities of the Philadelphia Academy of Music and was a frequent guest conductor at the Philadelphia Grand Opera. During that time he also participated in opera festivities at Covent Gargen in honor of King Edward VIII's coronation and Wagner performances at the San Francisco Opera from 1936-1938.

In 1938 Reiner was appointed conductor and music director of the Pittsburgh Symphony, resigning in 1948 over financial disputes. He became conductor at the Metropolitan Opera in New York City where he debuted with an historic performance of Strauss' Salome on February 4 1949. Among the 113 performances conducted during that brief tenure were acclaimed performances of Tristan und Isolde and Der Rosenkavalier and the organization's premiere of Stravinsky's The Rake's Progress.

From 1953-1962 Reiner conducted the Chicago Symphony. He died in New York City on November 15 1963.