At the heart of Ardglass is one of Northern Ireland's main fishing harbours - home port to about 30 fishing boats and landing point for fish caught by many craft of the County Down fishing fleet from in Portavogie and Kilkeel.
The natural deep water harbour has been used for 3,000 years. An important centre for the Gaelic Dál Fiatach clan who rules Lecale for 1,500 years and provided many kings of Ulster and High Kings of Ireland. Many descendants of the Dál Fiatach clan still live in the area with names like MacCartan, Magennis, Dunleavy, MacAonghusa, Magennis, Haughey, O'Hoey, Hoy, Ennis to name but a few. Families with these surnames can still be found in the area.
A surprise attack by the renegade Norman knight John de Courcy in 1177 seized Downpatrick. The Normans developed Ardglass along with Carrickfergus to be their main ports in Ulster. Many families with Norman names still live in the area like Fitzsimons, Savage, Denvir, and others.
After the confederate wars of the 1640s the town fell into the hands of the Irish. The English withdrew from the town and it gradually fell into decay. The owners throughout this era were the Earls of Kildare. In 1789 the son of the earl Rear Admiral Lord Charles FitzGerald made the Manor of Ardglass home. He sold this to his stepfather William Ogilvie in 1806.
For William Ogilvie his first project was to establish a harbour at Ardglass. The act was passed in Parliament in 1813. From the revenue of the harbour the town of Ardglass was rebuilt in Georgian splendour. The migratory herring season on the Irish Sea soon established Ardglass as a base. An extension to the harbour was begun in the 1830s but disaster occurred in 1838 when the new pier and lighthouse felt the brunt of a storm and fell into the harbour. After many years the pier was rebuilt and was extended again in the late 20th Century.