Material remains suggest that Koroni, considered to be the continuation of the ancient settlement of Asini, was inhabited since antiquity. The establishment of the castle probably dates to the Early Byzantine era. The Arab geographer Muhammed al-Idrisi, in the 12th century, speaks of “a small city with a fortress above the sea”. Owing to its central geographical location, Koroni was frequently targeted by pirates and aspiring conquerors.

In 1205, the castle, described as “powerless” in the Chronicle of the Morea, was captured without much difficulty by the Franks. A year later, Koroni passed to Venetian hands. In 1209, Venice’s sovereign rights in the region were officially ratified by the Treaty of Sapienza. The Venetians transformed the “powerless” fortress into a formidable seaside stronghold, which safeguarded a vital harbour for the Serenissima’s commercial activities in the Mediterranean.

During the first period of Venetian rule (1209–1500), Koroni flourished as a port, which was a mandatory stop for both merchants and ships carrying pilgrims to and from the Holy Land. Their accounts describe Koroni as a thriving city with a mixed Latin and Greek population. A suburb, or borgo, also developed outside the castle walls, towards the harbour. Compared to Methoni, its neighbouring “twin” Venetian colony, Koroni seems to have had a larger population and greater wealth. A Venetian document of 1348, written during the difficult years following the Black Death, notes that “Koroni always has an economic surplus, unlike Methoni, which remains in deficit”. Exports were key to the prosperity of the two cities, with products such as olive oil being a major export for Koroni and its region.

After the capture of Methoni by Sultan Bayezid II and the massacre of its inhabitants in August 1500, the people of Koroni, fearing a similar fate, surrendered to the Ottomans. Many chose to flee, seeking refuge in the Venetian-ruled Ionian islands, mainly Zakynthos and, somewhat later, Kefalonia. Between 1532 and 1534, in retaliation for the Ottoman attacks on Vienna, Andrea Doria, a Genoese admiral in the service of Habsburg Emperor Charles V and allied with the papacy and the Knights of Malta, captured Koroni. Upon his withdrawal, he was accompanied by more than 2,000 residents who settled in southern Italy.

In 1685, Francesco Morosini, head of the Venetian expeditionary fleet for the recovery of the Peloponnese, besieged and occupied Koroni, restoring it to the Venetians for a brief, 30-year period. In 1715, the Ottomans recaptured it, along with the rest of the Peloponnese. During the Orlov Revolt in 1770, the castle sustained damage by bombardment. Six years later, the French traveller Choiseul-Gouffier described a “terrified city” that had not yet recovered from the Orlov shelling.

In 1828, the Ottomans surrendered the castle to the French expeditionary force under General Maison and shortly thereafter was handed over to the newly established Greek state. During World War II, it served as a base for the Italian and German occupation forces. On their departure, the German troops detonated their ammunition stored in the northeastern bastion, destroying it. Today, Koroni is the only castle in Messenia that remains inhabited.