Dunaneeny was established by Alexander MacDonnell on a commanding headland above the bay then known as Port Brittas, the safe harbour where Hebridean galleys from Kintyre and the Inner Hebrides could be drawn up under the cliffs. The castle's strategic logic was simple. By controlling the bay, the MacDonnells controlled the choke point that connected their territories in the Scottish Isles to their growing landholdings in the Glens of Antrim. Tradition holds that an older castle once stood here, built by the O'Carrolls, an Irish family that had held the area before the MacDonnells. Modern excavation has gone further still, finding evidence that the same triangular headland was occupied as a late prehistoric or protohistoric promontory fort, possibly thousands of years before the MacDonnell stones went up.

Tradition names Dunaneeny as the birthplace of Sorley Boy MacDonnell, born around 1505, the man who would become the most famous chieftain in Antrim history. Sorley Boy survived the Battle of Glentaisie in 1565 just outside Ballycastle, where his brothers James and Angus were killed and captured by Shane O'Neill. He spent twenty years afterwards rebuilding MacDonnell power against the O'Neills of Clandeboye, the MacQuillans, and the English. He finally won official recognition of his claim to Ballycastle and the Route in 1586, after holding out long enough for the English to negotiate rather than fight. Eighty-five years old by then, he had outlasted nearly every enemy he had ever made.

The grimmest moment in Dunaneeny's history did not happen at the castle itself but in front of it, on the sea below. In 1575, an English force under the command of John Norreys, sent by Walter Devereux, Earl of Essex, sailed to Rathlin Island. Sorley Boy MacDonnell had moved his women, children, and elderly retainers to the supposed safety of the island. The English landed and slaughtered them. Several hundred non-combatants died. According to letters Essex wrote home to Queen Elizabeth's spymaster Sir Francis Walsingham, Sorley Boy watched the massacre from the cliffs of Dunaneeny on the mainland, helpless, the six miles of sea between him and his family a distance no man could close. Essex boasted to Walsingham that Sorley Boy was 'like to run mad from sorrow'. The phrase, written in a Tudor diplomatic letter four hundred and fifty years ago, still does the work of describing what cruelty against innocents looks like when seen from a great distance.

Sorley Boy MacDonnell died at Dunaneeny in 1590. Local tradition tells of a funeral procession that carried his body down from the headland, through Ballycastle, to his final resting place in the locked vaults of Bonamargy Friary on the eastern edge of town. He had outlived three brothers, two wives, and most of his rivals. Within a decade of his death, his son Randal MacDonnell - later created 1st Earl of Antrim - was rebuilding Dunaneeny, adding substantial timber-framed structures in the fashionable English style of the period. The MacDonnells had become English aristocrats while remaining Scottish-Irish chieftains. They would shortly move their main residence south to Glenarm Castle, which is where the family still lives today.

The castle that stands today is a scheduled monument under the Northern Ireland Department for Communities. The remnants sit on a near-triangular headland behind a caravan park, enclosed by a deep ditch cut into the rock. Visitors find the foundations of the gatehouse, sections of stone wall about two metres high and a metre thick, and faint traces of two other structures in the interior. It is not a tidy site. The Atlantic batters the cliffs below. Grass and wildflowers grow over the lower courses of stone. From the edge, the view runs out to Rathlin Island, to Fair Head's basalt columns, and on a clear day to the Mull of Kintyre. Sorley Boy's view, from the spot where he watched a massacre and from the room where he eventually died, is unchanged. It is one of the great views of Northern Ireland, with a heavy history.