A successful solo and orchestral cellist in his early life, Wallenstein took up conducting in the 1930s and served as music director of the Los Angeles Philharmonic from 1943 to 1956.
His family was of Austrian descent, having immigrated to the United States in the 1880s, and was descended from Albrecht von Wallenstein, a noted military commander in the Thirty Years' War.
[3] By his early teenage years, he had found work in Clune's Theater on Broadway, where he caught the attention of the impresario Lynden Behymer.
Owing to Behymer's connections, Wallenstein was given performance opportunities in high-profile clubs, as well as pit orchestras for silent films, where he became a personal favorite of prominent actors including Mary Pickford and Douglas Fairbanks.
He subsequently toured South America with Russian ballerina Anna Pavlova, whom Wallenstein had impressed after accompanying her on a performance of "The Swan" by Camille Saint-Saëns.
While there, Wallenstein studied with the German cellist Julius Klengel and briefly attempted to earn a degree in medicine at his father's urging.
Wallenstein returned to the United States after two years in Germany, and through Klengel's influence, he was appointed principal cello of the Chicago Symphony Orchestra under Frederick Stock.
During his tenure, Wallenstein championed the works of American composers, including Aaron Copland, Morton Gould, and Samuel Barber.
These included concerts with the New York Philharmonic, Philadelphia Orchestra, Symphony of the Air, and a stint as director of the Caramoor Summer Music Festival from 1958 to 1961.
2 featuring pianist Eugene List, an album of waltzes by Pyotr Ilyich Tchaikovsky, and Rachmaninoff's Symphony No.2 for Capitol Records in their FDS series.