Toscanini, also a cellist, advised Wallenstein to become a conductor. He conducted the Hollywood Bowl Orchestra and then conducted frequently on the radio. From 1943 to 1956, he was music director of the Los Angeles Philharmonic. He later taught at the Juilliard School in New York, where he died in 1983 at age 84.
In 1941, Wallenstein was given a personal Peabody Award for Outstanding Entertainment in Music.