The castle belonged to the Stewarts, but in 1570 it passed to the Montgomeries. A Cunningham, one of the tobacco lords, bought it in 1779 from Sir Walter Montgomerie-Cunninghame who had been impoverished by the American War of Independence. The present mansion was built around 1800; in 1824 a Tudor-Gothic extension was added.
Lainshaw Castle was described by Pont in 1608 as 'a stronge old Dunijon'.
In the present structure most of the ground floor walls and the south east wall face to a height of over 11.0 metres (36.1 ft) belong to the original castle. Two small ground floor windows and a larger third floor window with roll moulding are prominent among features remaining.
The surviving walls have been pierced by various doorway, providing access to later structural additions, with some subsequently being blocked. Three different rooflines are may be seen on the south east wall face. While there is little sound dating evidence for this structure, it is thought to date from between the late 15th century to the early 16th century.
- Coventry, Martin (2001). The Castles of Scotland. Musselburgh: Goblinshead. p. 2233 ISBN 1-899874-26-7
- "Lainshaw House". Royal Commission on the Ancient and Historical Monuments of Scotland. Retrieved 2016-11-28.
- "British Listed Buildings". British Listed Buildings. Retrieved 2016-11-29.