The building and Collegiate Church are at the heart of the medieval town, and are part of the UNESCO World Heritage Site of the "Historic Centre of San Gimignano".

[3] Further expanded in the 14th century,[4] the facade is characterised by arched windows, with the lower half of the frontage built with stone, and the upper part in brick.

The Civic Museum of San Gimignano is located on the upper floors of the building and can be accessed both from the Piazza del Duomo and from the courtyard behind the Palace.

Commissioned in 1317 by Nello de Mino Tolomei (then podestà of San Gimignano), the fresco is believed to have been inspired by the one painted by his brother-in-law Simone Martini's Maestà from the Palazzo Pubblico in Siena.

[9] The fresco shows Mary seated on a throne surrounded by adoring saints and angels (including patron Nello de Mino Tolomei).

It contains the ancient carved and inlaid wooden seats (1475) and a bust of San Bartolo in coloured terracotta of the first half of the fifteenth century within a niche.

Other rooms contain a Maestà from the late thirteenth century, altar decorations by Memmo di Filippuccio, a Madonna and Child by Vincenzo Tamagni (1528), several Gothic altarpieces (including one showing scenes from the life of Saint Gimignano), a Madonna with Saints Gregory and Benedict by Pinturicchio, and two medieval crucifixes of the Florentine school.