This sacristy was designed by Brunelleschi in the years between 1420 and 1429. It is a Renaissance building, a harmonious unified construction based on regular geometrical figures, the square and the circle.

The principal dome is divided into twelve segments, symbolising the twelve Apostles, while the small dome of the apse shows frescoes of the heavens and the signs of the Zodiac. The apse itself has three niches, an allusion to the unity of God in the Trinity. The polychromatic decorations, with stories of St John the Evangelist, and of the four Evangelists, are the work of Donatello.
He also cast the two doors in pure bronze. They are named after the figures they portray: the door on the right is the Door of the Martyrs and the one on the left is the Door of the Apostles.