According to Pliny the Elder, Portofino was founded by the Romans and named Portus Delphini, or Port of the Dolphin, because of the large number of dolphins that inhabited the Tigullian Gulf.
The village is mentioned in a diploma from 986 by Adelaide of Italy, which assigned it to the nearby Abbey of San Fruttoso di Capodimonte. In 1171, together with the neighbouring Santa Margherita Ligure, it was included in Rapallo's commune jurisdiction. After 1229 it was part of the Republic of Genoa. The town's natural harbour supported a fleet of fishing boats, but was somewhat too cramped to provide more than a temporary safe haven for the growing merchant marine of the Republic of Genoa.