Located next to Palazzo Chigi, in the historic city centre of San Quirico d'Orcia and overlooking the Via Francigena, the Collegiata church was built in the 11th century upon an old baptistery made of travertine. Its three doorways make it distinctive: the main one, which is also the oldest, consists of a slightly jutting porch with a round arch, decorated and supported on two sandstone columns knotted in the centre and resting on lions. In the second half of the 13th century, two additional doors were opened on the side of the church facing the Via Francigena. The first of the side portals is attributed to Giovanni Pisano, who was busy working on the construction of the Siena Cathedral at the time. The third door on this side, a work of the parish priest Lotto, features a combination of Romanesque and Gothic elements.
The bell tower as it appears today was built at the end of the 18th century and replaced an older one. The Baroque choir was built in 1655, replacing the original apse, while the high altar is in the Rococo style.
Two elements deserve a special mention: the wooden inlaid choir by Antonio Barili date from between 1482 and 1502, originally made for the Siena cathedral and then purchased by marquis Chigi for the Collegiata, and a triptych by Sano di Pietro, painted in the XV century for this church.