He began his career as an opera conductor, but he was later better known as a conductor of symphonic music. Between and he was director of the Kroll Opera in Berlin, where he presented new works and avant-garde productions of classics. He was from a Jewish family, and the rise of the Nazis caused him to leave Germany in Shortly afterwards he was appointed chief conductor of the Los Angeles Philharmonic , and guest-conducted other American orchestras, including the San Francisco Symphony , the New York Philharmonic and later the Pittsburgh Symphony , which he reorganised as a permanent ensemble.
In the late s Klemperer became ill with a brain tumour. An operation to remove it was successful, but left him lame and partly paralysed on his right side.
Throughout his life he had bipolar disorder , and after the operation he went through an intense manic phase of the illness and then a long spell of severe depression. His career was seriously disrupted and did not fully recover until the mids. He served as the musical director of the Hungarian State Opera in Budapest from to Klemperer's later career centred on London.
In he began an association with the Philharmonia Orchestra. By that time better known for his readings of the core German symphonic repertoire than for experimental modern music, he gave concerts and made almost recordings with the Philharmonia and its successor, the New Philharmonia, until his retirement in His approach to Mozart was not universally liked, being thought of by some as heavy, but he became widely considered the most authoritative interpreter of the symphonies of Beethoven , Brahms , Bruckner and Mahler.
When Klemperer was four the family moved from Breslau to Hamburg, where Nathan earned a modest living in commercial posts and his wife gave piano lessons.
