Saint John the Baptist's artificially posed figure is confined in a space that seems too small to contain his muscular frame. His torso twists to bring it parallel with his bent leg and arm, thus exposing a portion of his back. Although unnaturally posed, Agnolo Bronzino's serpentine figure of Saint John achieves a graceful fluidity typical of the style called Mannerism.

The unusually tall format of this work results from its original position as the left panel of the altarpiece in the private chapel of Eleonora da Toldeo in the Palazzo Vecchio. Representing the patron saint of Florence, this panel was paired with one of Saint Cosmas, the name saint of Eleonora's husband, Cosimo de' Medici.