He started as a violinist but the Belgian-born violist, conductor and educator Léon Barzin advised him to switch to viola.
He joined the NBC Symphony Orchestra in 1943, replacing the well-known William Primrose on the first-desk of the section.
During his decade with the orchestra, Katims developed a close relationship with conductor Arturo Toscanini and became his assistant.
He organized a series of chamber music concerts titled Candlelight Musicales, in the Spanish Ballroom of the Olympic Hotel, with visiting soloists such as violinist Isaac Stern, cellist Leonard Rose and pianists Leon Fleisher and Claudio Arrau.
His influence enabled the school to attract and hire several notable musicians, such as Carlisle Floyd, Elena Nikolaidi, and Abbey Simon, to the faculty.