During the late 1930s Byas played in several swing bands, including those of Don Redman and Andy Kirk, and in 1941 he became a tenor saxophone soloist (as in “Harvard Blues”) with Count Basie (Basie, Count). He also became associated with bebop innovators such as Charlie Parker (Parker, Charlie) and Dizzy Gillsepie (Gillespie, Dizzy). In small groups (1943–46) led by himself and others, Byas experimented with the new concepts of bop harmony and rhythm. His 1945 duets with bassist Slam Stewart, “Indiana” and “I Got Rhythm,” show his fluent style with long lines founded in Coleman Hawkins (Hawkins, Coleman)' rich tone and phrasing but including modern bop harmonic elements.

In 1946, with a Redman band, Byas went to Europe, and he remained there, living in France, The Netherlands, and Denmark for the rest of his life. He continued to pursue a freelance career, touring and recording often, but he only revisited the United States once, for a tour in 1970. Performances such as A Tribute to Cannonball (1961) reveal continuing swing and creative vigour in his later years.