The name Deganwy has been interpreted in modern times as Din-Gonwy, which would mean "Fort on the River Conwy", but the historical spellings make it impossible for this to be the actual origin of the name although mentioned in Domesday Book is "the territory of the Decanae tribe".

Deganwy formed part of the ancient borough of Conwy from medieval times.

Deganwy appears to have been the capital of Gwynedd at this time, but this was later moved to Aberffraw on Anglesey.

The London & North Western Railway built at Deganwy a rail-connected riverside quay and wharves (occasionally referred to as St George's Dock), largely for the purpose of exporting slate by coastal steamer.

A marina with its accompanying housing and hotel accommodation was established on the site of the former slate wharfs early in the 21st century.