Italian Gothic painter of the Sienese school who with his brother Ambrogio was the principal exponent of Sienese secular art in the years before the Black Death. Little is known of Lorenzetti's life, and the attribution and dating of many of the works associated with him remains hazardous.

He was probably a pupil of Duccio, whose influence is seen in the graceful linearity and rich colour of Lorenzetti's earliest documented work, the altarpiece (1320) in the Pieve di Sta. Maria, in Arezzo. But the altar's centrepiece, a “Madonna and Child,” replaces Duccio's frigidly hierarchical conception of the subject with an intimate depiction of an affectionate mother caressing her mischievously playful baby. Those features, combined with the wealth of decorative detail (recalling Simone Martini) and the plasticity of the figures (derived from Giovanni Pisano), lend the painting a vivacity rare in contemporary Sienese art.

Sometime during 1330–40, Lorenzetti worked on a number of frescoes in the lower church of S. Francesco, in Assisi. The “Deposition,” in its clarity of composition and the monumentality of the sculpture-like draperies, shows a sensitive response to the art of Giotto. Lorenzetti's figures achieve corporeality by means of strong, only partly blended colours. The “Madonna and Child” in the same cycle, however, returns to the intimacy of the Arezzo altarpiece in the Child's exuberance and the Madonna's reproving look and abrupt gesture toward St. Francis. It is in such scenes as the “Last Supper” that he departs most strikingly from Giotto. He abandons Giotto's unity of time and place and compositional clarity in favour of carefully rendered minutiae and nonessential anecdote. That love of detail intrudes upon the otherwise Giottesque “Crucifixions” in S. Francesco, Siena, and Museo Diocesaro, Cortona.

Lorenzetti's mature style is epitomized in the triptych “Birth of the Virgin” (1342; Museo dell'Opera del Duomo, Siena), his last major work. That he used the decorative detail and familial anecdotes as the theme of a major altarpiece is illustrative of his nonhierarchical, humanizing tendencies. Perhaps the most notable feature of the “Birth” is its sophisticated handling of perspective and the logical placement of figures within space. The arches and colonnettes of the triptych frame form the foreground of the painted picture space, and one of the figures is painted in such a way that it appears to be standing behind one of the colonnettes. This constitutes one of the most advanced perspective studies of its time.