One of the most original and influential painters of the fourteenth-century Sienese school, His art owes most to Duccio though there is no evidence that he was Duccio’s pupil. He may have been a pupil of Memmo di Filipuccio, whose daughter he married, thus becoming a brother-in-law of Lippo Memmi. In 1315 he signed and dated the fresco of the Majestas in the Siena Palazzo Pubblico, one of his most important works and the earliest known; it has been extensively repainted, once by Simone himself, and is in deplorable condition. Soon after this work he probably went to Naples, and his picture of St. Louis of Toulouse Crowning Robert of Anjou (c.1317) is in the gallery there. His influence on local fresco painters in Naples attests to his presence in the area. In 1320 he painted a polyptych for the church of St. Catherine at Pisa (a major part of it is preserved in the Municipal Gallery and the Seminario) and a Madonna and Saints for the cathedral of Orvieto (now in the Opera del Duomo). Works of Simone’s school are found in both Pisa and Orvieto. In 1321 he was back in Siena and painted a Madonna (now lost) for the Chapel of the Nine, and the next year was at work in the Palazzo Pubblico of his home city.
A considerable time between 1320 and 1325 was probably spent in Assisi, where he executed a fresco cycle on the life of St. Martin in the Lower Church of San Francesco. In this work he first manifests a close relation with French Gothic painting, examples of which he could have seen at Assisi. In 1325 he was again in Siena, painting for the palace of the Capitano del Popolo, and in 1326 he was employed by the Commune as an architect. In 1328 he painted in fresco the important equestrian portrait of Guidoriccio dei Fogliani da Reggio, Sienese captain general and hero, in the Palazzo Pubblico. In 1333 he signed, together with Lippo Memmi, the famous Sant’ Ansano Annunciation (painted for the Siena cathedral and now in the Uffizi) a work which had tremendous influence all over central Italy. In 1339 he left for the papal court at Avignon and was destined never to return to Italy. His patron at Avignon was Cardinal Jacopo Stefaneschi. He painted frescoes in the cathedral, became a friend of Petrarch’s and is known to have painted a portrait of Petrarch’s Laura (now lost). Assisted by Matteo da Viterbo and a host of other painters from both Italy and France, he established a flourishing school in Avignon. There is practically nothing left of his work there, but an example from this period is the signed panel (1342) of Christ Returning from the Temple, now in the Liverpool gallery. A signed but dismembered polyptych with scenes from the live of Christ (preserved in Antwerp, Berlin and the Louvre) dates from this late period. These two works reveal his late style as marked by Gothic flamboyance and extreme emotional exaggeration, in contrast to the delicate lyricism of his earlier periods. The influence of his late work on northern European painting was tremendous. Simone was a master of technique and evidenced the Sienese love of precious material preciously used. He introduced the fresco technique into the Sienese school, but his own frescoes have suffered from the fact that he painted or retouched many portions a secco (i.e., on a dry surface) instead of in true fresco on wet plaster. His style is characterized by its seriousness, aloofness, aristocracy and spirituality. The linear quality of the tradition of Duccio achieves its highest expression in his work.