Peter III of Aragon (1239 - November 11, 1285, also Peter I of Valencia, Peter II of Barcelona), known as the Great, was the king of Aragon and Valencia and count of Barcelona from 1276 to 1285.

In 1262, he married Constance, daughter and heiress of Manfred of Sicily. He became Peter I of Sicily from 1276 after the Sicilian Vespers expulsed the French from the island. His navy under the admiral Roger of Lauria defeated the invading French crusade at Roses, and his armies crushed the retreating French crusaders at the Coll de Panissars in 1285.

Peter left Aragon to his eldest son Alfonso III of Aragon, and Sicily to his second son James I of Sicily.

In the Divine Comedy Dante sees Peter "singing in concert" with his former rival Charles I of Sicily outside the gates of Purgatory.