Saint John the Evangelist is shown writing the Book of Revelation, the final book of the New Testament, with his symbol, an eagle, at his side.
Saint John looks up at his vision of the Woman of the Apocalypse (Revelation 12), which was the source for much of the imagery associated with the Immaculate Conception. This provides the thematic link between this work and its companion piece, 'The Immaculate Conception'.
As in all Velázquez's early work, the central figures in both works are painted from models. The Saint John here is less idealised than the Virgin depicted in 'The Immaculate Conception'.