Sir William Douglas, 4th Baronet (c. 1730 – 16 May 1783) was a Scottish politician who sat in the British House of Commons from 1768 to 1780, representing the constituency of Dumfries Burghs.

He succeeded his uncle Charles Douglas, a wealthy East India Company merchant to his Breconwhat estate in Dumfries in 1770.

Sir William later commissioned the building of Lockerbie House.

He was also a favourite of his relative the Duke of Queensberry, who bequeathed to him £16,000 upon his death in October 1778.

Together, they were the parents of five sons and four daughters, including:[1] Sir William died on 16 May 1783.