The son of Sir John Adam, 9th Bt., and Anne (née Napier) Hay, Sir Duncan Edwyn Hay succeeded his father as 10th Baronet in 1895. He was educated at Eton, and served in the Royal Company of Archers (the Queen's Body Guard for Scotland). From 1914-15, he was a Lieutenant in the Royal Marines; from 1917-18, an Aide-de Campe, Personal Staff; and was also a late Lieut. of the 3rd Battalion, Royal Scots Guard. On 12 December 1905, he married Lavinia Mary [d. 1958], daughter of Wallace Charles Houston. He married secondly on 4 Sept. 1958 to Isobel Rose, daughter of Sir Alexander Walker. Having no children, Sir Duncan was succeeded in the baronetcy by his cousin, Sir Bache McEvers Athole Hay.
Blair, Claude. The James A. de Rothschild Collection at Waddesdon Manor: Arms, Armour and Base-Metalwork. London and Fribourg, 1974: 46-52.