Archaeological finds demonstrate the presence of Celtic settlement in the area before the arrival of the Romans. The latter built a castrum here and made it an important road hub. After the fall of the Western Roman Empire, the Lombards captured the town in the 6th century; they were followed by the Franks, who made Lecco the seat of a countship and, later, of a frontier Mark.
Emperor Otto I spent a long time in Lecco, quenching the 964 revolt against the Holy Roman Empire led by Lecco’s count Attone. Later it became a possession of the Milanese monastery of St. Ambrose. Conrad II also stayed in Lecco, in the attempt to free it from the church, but as the result of the ensuing wars the city was subjected by Milan. It subsequently followed the history of the Duchy of Milan and of Lombardy. In the early 16th century it was briefly ruled by the condottiere Gian Giacomo Medici.
During World War II it was an important centre of the partisan war against the German occupation