The church, begun in 1492, was brought to a close in 1656 with the addition to the gable elevation bipartite by pilasters, a portico with three openings. The porch is of later construction.
The interior, with a Latin cross plan, is decorated with frescoes of the seventeenth century Sienese school, including: the Dream of sant’Irenedi Stefano Volpi, the Glory of St. Sebastian and the Virtues and angels by Sebastiano Folli, the Stories of St. Sebastian by Pietro Sorri and Rutilio Manetti. In the chapel of the Banner is a copy of the Banner of St. Sebastian of Sodom (the original is in the Uffizi). The four coffin heads on the walls are attributed to Girolamo Pacchia. In the chapel to the right a Madonna by Francesco Rustici.
In the high altar, in addition to the dispossession of Christ by Luigi Ademollo, a fifteenth-century crucifix which according to legend St Bernardino would donate to the Society of St. John the Baptist Death.