Mauchline Castle is an altered 15th century keep, to which has been added a 17th century L-plan wing, as well as other extensions and alterations of 1690, 1800 and 1820. The arms of Abbot (of Melrose) Hunter (died 1471) adorn the building.
The basement and hall on the first floor are both vaulted, but the inside of the castle has been much altered.
The castle was built by Melrose Abbey to manage its Ayrshire estates. It passed to the Campbells of Loudon after the Reformation and was used as the factor's house. Robert Burns paid his rent here, and was married in one of the extensions to the keep. The castle is in good condition.