He was Earl of Douglas and 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 Seigneur of Dun-le-roi in France.

In contemporary French sources, he was known as Victon, a phonetic translation of his Earldom of Wigtown.

Douglas served as ambassador to England in 1424, during the ransoming of King James I of Scotland.

They had three children: Both sons were summarily beheaded at Edinburgh Castle on trumped-up charges, in the presence of the child king James II.

The "Black Dinner" led to the lordships of Annandale and Bothwell being annexed by the crown, Galloway to their sister, Margaret Douglas, and the Douglas lands and earldom passed to William's great-uncle James Douglas, Earl of Avondale, who was himself implicated, with Sir William Crichton, in the murder of the young earl.