He was born in Odessa on November 17, 1899. A student of Leopold Auer in St. Petersburg, Seidel became known for a lush, romantic tone and unique and free rubato. In the 1930s he emigrated to the United States, making his way to Hollywood where he made a career in the studios of motion pictures. He was featured (as soloist) in several Hollywood productions, including the movies Intermezzo, Apomethe,  and Melody for Three.  He was also an avid chess player (like Mischa Elman).
Seidel performed on violins by Antonio Stradivari "Da Vinci" 1712 (now known as the Ex-Seidel), Giovanni Battista Guadagnini 1786 (now known as the Ex-Seidel), as well as copy of the "Alard Stradivari" by Jean-Baptiste Vuillaume 1860.
He died on November 15, 1962.
- "The boy (Jascha Heifetz) was one of those in a group of young Jewish violinists who later startled the world. The others would include Mischa Elman, Tosha Seidel, Efrem Zimbalist and Nathan Milstein." —New York Times by Harold Schonberg, Published: December 12, 1987