A small number of early documents list payments to a William Cornysh for compositions, and for participation in courtly dramas and "disguysings," the earliest dating from 1494. He spent time in prison starting in 1502, producing a pamphlet of versified defenses while incarcerated. Apparently his term was brief, as his 1501 appointment as a Gentleman of the Chapel Royal was never revoked, and he was appointed Master of the Children for the Chapel establishment in 1509, a position he held until his death in 1523. Records of court dramatic presentations in 1511 and 1514 credit him with musical collaboration, and his presence leading the royal singers across the Channel in 1513 and again at 1520 during the celebrations on the field of the Cloth of Gold is well-documented. As late as June 1522, the court received a play of his, celebrating the diplomatic visit by the Holy Roman Emperor.
The surviving sacred music of "Cornysh" in the Eton Choirbook shares with much of that repertory a thick, melismatic texture, a noble breadth of vocal range, and a penchant for biting cross-relations and other dissonances. His splendid and popular setting of the Marian text "Salve regina" from this source exemplifies the style. Indeed, his contributions to this volume bespeak a surprising maturity of hand. In his time, however, William Cornysh Jr. (presuming that both repertoires are his) seems to have been far better known for his secular work, as a song composer, actor, playwright, and stage director, and one at the center of the Tudor court's secular culture. A song of his from Henry VIII's Songbook, A robyn, gentle robyn, may have been the song Shakespeare intended the clown to sing in the fourth act of Twelfth Night.