By the end of the 19th century, he was playing with Arnold Schoenberg, Arthur Bodanzky, and Edward Falck in a local string quartet.

In 1907, Riesenfeld emigrated to New York City, where he worked until 1911 as concert-master for Oscar Hammerstein's Manhattan Opera Company.

Samuel Lionel Rothafel—later known as "Roxy" Rothafel—hired Riesenfeld in 1916 as conductor of, successively, the Rialto, the Rivoli, and the Criterion theatres until 1925, introducing the practice of long-run resident film musicians.

On 15 April 1923, with inventor Lee de Forest, Riesenfeld co-presented a show at the Rivoli Theater in New York City of 18 short films made in the Phonofilm sound-on-film process.

In 1923, Riesenfeld formed The Red Seal Pictures Corporation, partnered with Edwin Miles Fadiman, Dr. Lee deForest, and Max Fleischer to distribute American and foreign films through their chain of 36 theaters that extended as far as Cleveland, Ohio.

In May 1926, Max Fleischer began producing a series of sound versions of their popular "Bouncing Ball" Song CarTunes, using the Lee de Forest Phonofilm sound-on-film process.

Next to Albert William Ketèlbey and Ernö Rapée, Riesenfeld was a pioneer of modern, high-quality production of music.

When he wrote the music for the Western movie The Covered Wagon (1923), Riesenfeld was one of the most frequently employed film composers in Hollywood.