In 1959, he began performing as "Horacee" when he joined a big band led by David Baker; he also played with Roland Kirk and Charles Mingus that year.
Throughout the 1960s, he worked in jazz with pianist/composer Hasaan Ibn Ali and bassist Henry Grimes, and with the Bud Powell Trio at Birdland.
Later in the 1960s, he played with Hugh Masekela and Miriam Makeba; following this he studied composition under Heiner Stadler, Hy Gubenick, and classical guitar with Ralph Towner.
In the 1970s, Arnold became one of the best-known jazz fusion drummers, playing with Return to Forever, Stan Getz, Archie Shepp, and Billy Harper in addition to releasing two of his own solo albums.
He worked as a session musician, played with Kenny Burrell, and formed a trio with David Friedman and Anthony Cox.