Built in 1430, Borthwick Castle remains largely unchanged, although it has undergone some restoration over the centuries. The main rectangular block features two full-height protruding towers, and the whole structure is surrounded by a wall strengthened with towers.

The castle occupies a raised position, and is built on the site of the motte of Lochorwart. Evidence of the motte can still be seen in the form of terracing to the east measuring around 4.0 metres wide by around 1.3 metres high.