The lands of Cathcart were held by the family of that name from the 12th century. In the mid-15th century the head of the family was raised to the peerage as Lord Cathcart, and it is believed that the castle was built at around this time. In 1546 the castle passed to the Semple family. It is highly unlikely that Mary, Queen of Scots, would have spent the night before the Battle of Langside (1568) at Cathcart Castle or have watched the battle from a nearby hill called the Court Knowe. The Semples were supporters of Mary's enemies and would have captured her and put an end to her plans before the battle had started. Court Knowe is some 60m below the height of Langside village, where the battle took place, meaning Mary would not have been able to see what took place. A more likely site would have been Prospecthill, which lies on the line of her army's approach to Langside.