Klemperer was born in Breslau. He studied music first in Frankfurt, and later in Berlin under Hans Pfitzner. In 1905 he met Mahler while conducting the off-stage brass at a performance of Mahler's Symphony No. 2 (Resurrection). The two became friends, and Klemperer became conductor at the German Opera in Prague in 1907 on Mahler's recomendation. Later, in 1910, Klemperer assisted Mahler in the premiere of his Symphony No. 8 (Symphony of a Thousand).
Klemperer went on to hold a number of posts, including conductorships at the Municipal Theatre in Hamburg (1910-12); in Barmen (1912-13); the Strasbourg Opera (1914-17); the Cologne Opera (1917-24); and the State Opera in Wiesbaden (1924-27).
From 1927 to 1931, he was conductor at the Kroll Theatre in Berlin. While there he enhanced his reputation as a champion of new music, playing a number of new works there including Leos Janacek's opera, From the House of the Dead, Arnold Schoenberg's Erwartung, Igor Stravinsky's Oedipus Rex and Paul Hindemith's Cardillac.
In 1933, with the Nazi Party in power, Klemperer, who was Jewish, left Germany to move to the United States and became conductor of the Los Angeles Philharmonic Orchestra. There he began to concentrate more on the standard works of the Germanic repertoire that would later bring him greatest acclaim, particularly the works of Beethoven, Brahms and Mahler.
Following the end of World War II, Klemperer returned to Europe to take up the baton at the Budapest Opera (1947-50). He was conductor of the Montreal Symphony Orchestra from 1950 to 1953 before moving to London and becoming the first principal conductor of the Philharmonia in 1959. He also worked at the Royal Opera House, sometimes stage directing as well as conducting, as in a 1963 production of Richard Wagner's Lohengrin.
Klemperer is less well known as a composer, but he wrote a number of pieces, including six symphonies, a Mass, nine string quartets, and an opera called Das Ziel.
Later in his life, Klemperer suffered from partial paralysis which had largely been brought on as a result of surgery in 1939 to remove a tumor on his brain, surgery which also made his bipolar disorder rather more prominent. Despite this he conducted until 1971, when he retired. He died in Zürich in 1973.
Klemperer made many recordings, and some have become classics. Worthy of note are: