Thirlestane Castle is a 16th century castle, the oldest part of which is a rectangular tower house or block of three storeys, which had a large tower at each corner. It was considerably enlarged in the 1670's with the re-building of the main block, heightening it to six storeys, and the addition of round turrets. Three semi-circular towers along each side contain stairs, as do many of the turrets. Parapets are supported on arches running along each side. A symmetrical forecourt was also added, with three-storey wings, which were extended in the 19th century.
The interior has been much altered. A fine 17th century plaster ceiling survives on the second floor, as do Baroque plaster ceilings elsewhere.
The original castle of the Maitlands stood two miles away at Old Thirlestane. The present castle was built by Sir John Maitland, James VI's Chancellor, but it was John Maitland, Duke of Lauderdale, a very powerful man in Scotland in the 17th century, who had the house remodelled in 1670 by William Bruce. Lauderdale was Secretary of State for Scotland from 1661 to 1680, but eventually replaced after the Covenanter uprising which ended with their defeat at the Battle of Bothwell Brig. His ghost is said to haunt Thirlestane, as well as St. Mary's in Haddington. Bonnie Prince Charlie stayed here in 1745 on his way south. The 19th century extensions were designed by David Bryce. The castle is still occupied by the same family.