The castle gained particular note in 1600 when it served as the residence of Phelemy Brasleigh O’Doherty, a member of one of Donegal’s most powerful Gaelic families. Following the Flight of the Earls and the subsequent Plantation of Ulster, the castle was granted to Arthur Chichester in 1611, who promptly leased it to a Lieutenant Hoan. This new tenant was contractually obligated to restore the castle and had already made significant progress, completing what contemporary records describe as ‘a good bawne of lyme and stone’; a defensive stone wall that would have enclosed the castle grounds.

The keep itself is a small, sturdy structure built from rubble stone with dressed corner stones, all bound together with a rough mortar made from sea sand. The walls show an unusual variation in thickness and feature a distinctive batter, or inward slope, up to the first floor level. What appears to have been the main entrance can be identified by a rough opening in the eastern wall, where protruding stones at ground level likely mark the foundations of the original splayed door frame. The castle’s defensive capabilities were enhanced during a second phase of construction, when a semi-circular tower was added to the southeast corner along with an adjoining wall that once extended eastward across the promontory for approximately 12 metres.

Today, visitors can still trace the outline of these defensive walls, whilst remnants of faced stonework survive precariously on the cliff edge, suggesting there may have been an additional wall or tower in this exposed position. About 11 metres north of the keep, a pile of rubble marks what was probably another structure within the castle complex, though its exact purpose remains unclear. These ruins offer a tangible connection to a turbulent period in Irish history, when Gaelic lordships gave way to English plantation, and ancient strongholds like Carrickabraghy found themselves repurposed for new masters and new purposes.