MacLellan's Castle, located in the centre of Kirkcudbright in Galloway, Scotland, is an L-plan tower house built in the late 16th century on the south bank of the River Dee. The site originally held a Greyfriars monastery, founded around 1455, which fell into ruin. In 1569 Thomas MacLellan of Bombie received the land, retaining only the chapel-now Greyfriars Church-and began constructing the castle around 1577. A carved date of 1582 above the entrance likely marks a key stage in the building's progress. Though the structure was never fully completed, it served as the residence of the MacLellan family until 1752, when it was sold to Sir Robert Maxwell; by then the roof had collapsed and the castle was already decaying. In 1782 the property passed to Dunbar Douglas, 4th Earl of Selkirk.

By the late 19th century the castle was heavily overgrown-MacGibbon and Ross described it in 1887 as a mass of ivy resembling a green haystack-yet structurally sound aside from the missing roof. Growing national interest in heritage protection led to its transfer into state care in 1912. Today it is managed by Historic Environment Scotland.

Architecturally, the four-storey castle comprises two wings meeting at right angles, enhanced by a southwest tower and additional projections. Typical of Scottish tower houses of the period, it features a ground-floor kitchen, a first-floor great hall, and upper-floor accommodation. Notable is the "Laird's Lug," a concealed listening chamber beside the hall's fireplace. Above the entrance, carved panels display the coats of arms of Thomas MacLellan and his wife, G. Maxwell.