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