Douglas was the eldest son of Sir Archibald Douglas of Glenbervie, Knt., by his spouse Agnes, daughter of William Keith, 3rd Earl Marischal, and upon the death of Archibald Douglas, 8th Earl of Angus without issue, William succeeded to that Earldom as heir-male, in 1588.
Sir Robert Douglas states that "Sir William Douglas of Glenbervie [as he was styled prior to his succession to the earldom] was a man of great honour and integrity, and a steady friend of Queen Mary. He accompanied her in her expedition to the north, and behaved with utmost fortitude and resolution at the fight of Corrichie anno 1562".
According to David Hume of Godscroft, Angus and Lord John Hamilton argued over precedence in the king's privy or outer chamber at Holyrood Palace. James VI came out of his bed chamber and made them reconcile. Meanwhile, Sir John Carmichael, Captain of the Guard, had made the palace secure, and Angus had to signal to his followers from a window that all was well.
Douglas died in July 1591, in his 59th year.
- William Douglas, 10th Earl of Angus, eldest son and heir,
- Archibald Douglas, Parson of Glenbervie (d. 1584).
- George Douglas (d. 1590), who attended James VI in Denmark.
- Sir Robert Douglas of Glenbervie, received from his father the lands of Glenbervie by charter dated 14 July 1592.
- Duncan Douglas, Parson of Glenbervie (d.1591)
- Gavin Douglas (d. bef 1 October 1616) who married Elizabeth Keith; ancestors of the family of Douglas of Bridgeford
- Sir John Douglas of Barras
- Francis Douglas (d.c. 1600)
- Henry Douglas of Tannachy (d. 5 October 1595) who married Janet Murray at sometime before 1580. Had issue Janet Douglas born 16 April 1580 Dunfermline Scotland.
- Margaret Douglas, married William Forbes of Monymusk
- Jean Douglas, married John Wishart of Balisycht
- Elizabeth Douglas, married Thomas Gordon of Cluny
- Sarah Douglas, married 1st Robert Strachan, 2nd George Auchinleck of Balmanno
- Burke & Burke 1848, pedigree CLXXXV.
- Anderson 1863.
- Douglas 1798, p. 19.
- David Reid, David Hume of Godscroft's History of the House of Angus, vol. 2 (Edinburgh, 2005), p. 418.
- One or more of the preceding sentences incorporates text from a work now in the public domain: Anderson 1863
- Fraser, vol ii,pp 377-378
- David Stevenson, Scotland's Last Royal Wedding (Edinburgh, 1997), p. 121.
- Fraser, Sir William, The Douglas Book (4 Vols). Edinburgh 1885 
- Burke, John; Burke, John Bernard (1848), The royal families of England, Scotland, and Wales: with their descendants, sovereigns and subjects, 1, London: E. Churton, pedigree CLXXXV
- Douglas, Sir Robert; et al. (1798), The Baronage of Scotland, Edinburgh, p. 19
- Anderson, William (1863), The Scottish Nation Or the Surnames, Families, Literature, Honours and Biographical History of The People of Scotland
- Burke, John; Burke, John Bernard (1851), The royal families of England, Scotland, and Wales: with their descendants, sovereigns and subjects, 2, London: E. Churton, pedigree CCVIII
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