The castle is a stronghold naturally bounded on the west by the River Nith, to the north by a burn, and made strong by a deep ditch running the remainder of the boundary. It was visited by many notable figures who appear in the history of the local area, including Robert the Bruce, William Wallace, Edward I, Mary Queen of Scots, and James VI.
Sanquhar Castle was sold by the Crichtons in the mid 17th century to Sir William Douglas, 1st Duke of Queensberry, who established the fairytale pink sandstone Drumlanrig Castle ten miles south of Sanquhar near Thornhill. From then on the castle at Sanquhar began to steadily crumble to a ruin, until 1895 when John Crichton-Stuart, 3rd Marquess of Bute, purchased it and attempted to enthuse a restoration of his ancestral home, following successful restorations at Cardiff Castle and Castell Coch in Wales. Sadly, work ended following his death in 1900, and what is left of the site is an odd mix of restoration and original stonework.