Italian architect, painter, and decorator, an outstanding exponent of Baroque style.

Pietro studied in Rome from about 1612 under the minor Florentine painters Andrea Commodi and Baccio Ciarpi and was influenced by antique sculpture and the work of Raphael. The most important of his earliest paintings were three frescoes (1624–26) in Santa Bibiana, Rome. In the 1620s he designed the Villa del Pigneto near Rome and possibly another villa at Castel Fusano, both for his patrons, the Sacchetti family.

His fame reached its climax in the 1630s with the design of the Church of SS. Luca e Martina, Rome (1635–50), and the ceiling fresco “Allegory of Divine Providence” (1633–39) in the Barberini Palace there. The design of SS. Luca e Martina derives more from Florentine than Roman sources, resulting in a different type of Baroque architecture from that of either Bernini or Borromini. The ceiling of the Great Hall in the Barberini Palace, now the National Gallery, was conceived as a painted glorification of the Barberini pope, Urban VIII, and is treated illusionistically. Its strong colour and steep perspective recall Veronese, whose work Cortona may have seen in Venice in 1637.

Also in 1637 Pietro visited Florence, where he began painting the frescoes representing the “Four Ages of Man” for Grand Duke Ferdinand II of Tuscany in the Pitti Palace. In 1640 he returned to finish these and paint the ceilings of a suite of apartments in the palace named after the planets. He treated the entire surface as a single spatial unit, adding a wealth of real stucco decoration, partly gilt, in the carvings. He returned to Rome in 1647, where he painted the vault frescoes of Santa Maria in Vallicella and the ceiling of the long gallery of the Pamphili Palace in Piazza Navona (1651–54) for Pope Innocent X. His chief architectural works of this period were the facades of Santa Maria della Pace (1656–57)—perhaps his most ingenious conception—and Santa Maria in Via Lata in Rome (1658–62). He also produced designs for the modernization of the Pitti Palace and the east front of the Louvre in Paris (1664). He painted religious and mythological easel pictures throughout his life. From 1634 to 1638 he was head of the Academy of St. Luke in Rome. Despite a correspondence in feeling between his architecture and his painting, there is little physical connection between them, and he never decorated one of his own churches.