The melody of “What Child Is This?” is taken from “Greensleeves,” a traditional English tune.
The carol’s words were written by William Chatterton Dix in 1865, originally as a poem titled “The Manger Throne.” The familiar pairing of Dix’s text with “Greensleeves” appeared in the influential collection Christmas Carols New and Old in 1871.
“Greensleeves” is much older than the Christmas carol and is often described as a traditional English folk song. Its authorship is uncertain, despite a longstanding popular claim that Henry VIII composed it. The melody’s haunting character helped give the Christian nativity text its distinctive sound.
A common mix-up is to treat “What Child Is This?” and “Greensleeves” as two unrelated melodies. They are separate works, but the carol uses the older tune. The arranger who made the pairing is not known with certainty, although John Stainer is often suggested.