William, 6th Earl of Douglas (c. 1424 – 24 November 1440) was a Scottish nobleman.

In addition to his Earldom of Douglas, he was Earl of Wigtown, Lord of Galloway, Lord of Bothwell, Selkirk and Ettrick Forest, Eskdale, Lauderdale, and Annandale in Scotland, and de jure Duke of Touraine, Count of Longueville, and Lord of Dun-le-roi in France.

He married Lady Janet Lindsay, daughter of David, Earl of Crawford, and succeeded to the earldom on the death of his father, who had served as regent of James II.

Together they conspired to break the power of the late Archibald Douglas's family, and summoned William and his younger brother David to Edinburgh Castle.

The so-called 'Black Dinner' which followed saw the two boys summarily beheaded on trumped-up charges, over the protests of the young King James II.