He is the son of Aonghas Óg, chief of Clan Donald (Clann Domhnaill), and claimant to the Lordship of the Isles, which had been held by his grandfather John of Islay, Earl of Ross (Eoin MacDomhnaill).
While just an infant, Domhnall Dubh is captured by Cailean I, Earl of Argyll, and imprisoned in Innischonnel Castle in Loch Awe.