American tenor saxophonist, a jazz musician noted for his devotion to purely lyrical improvisation.

Marsh played in Hoagy Carmichael's Teenagers (1945) before serving in the U.S. Army. In 1948 he became a student of Lennie Tristano (Tristano, Lennie), who was the principal influence upon his art. He played with Tristano from 1949 to 1952 and in rare reunions thereafter. On occasion he played with outstanding former Tristano students such as Lee Konitz and Ted Brown (tenor saxophone). For many years Marsh led his own small groups irregularly and taught; for about five years in the mid-1970s, he played in Supersax, a saxophone-centred ensemble, and orchestrated a number of Charlie Parker solos for the group.

Marsh shared Tristano's ideal of spontaneity. High rhythmic detail, swing, and a complex approach to harmony characterize Marsh's sophisticated solo lines, which he usually preferred to play over unaccented rhythm accompaniments, the better to focus attention on his fluent melodies. His tone was light, without dramatic inflection; as a result he was often considered a cool jazz soloist despite the passion of his quest for lyricism.