Jacopo Sansovino (1486-1570), also an important sculptor, was a Florentine who had already had a successful career in Florence and Rome. He fled to Venice after the catastrophic sack of Rome in 1527 and in 1529 was appointed chief architect (Protomaestro or Proto) of the Procurators of San Marco. His project to stabilize the long-problematic domes of St. Mark's by wrapping them with iron bands brought him a great reputation. He is responsible for the appearance of much of the area around Piazza San Marco, designing the Biblioteca Marciana (1537) and the Zecca in Piazzetta di San Marco. Among his palaces, the Palazzo Corner della Ca' Grande and the Palazzo Dolfin Manin stand out.

The Marciana Library is considered his great masterpiece and a key work in Venetian Renaissance architecture. Palladio, who saw it being built, considered the building "the best ever built since the times of the ancients."

Main buildings