During his father's chiefship, Duncan led an expedition against their rivals the Clan Cameron which had resulted in the Battle of Craig Cailloch in 1441.
Also before he became chief, he had fought a successful battle at Culloden against Gillespie MacDonald, brother of John of Islay, Earl of Ross who had stolen cattle from the Mackintosh lands of Petty.
Upon the first forfeiture of the Lordship of the Isles and its annexation of the Earldom of Ross to the Crown, James IV of Scotland granted a charter to Duncan dated 4 July 1476.
[1] Duncan also seems to have been on excellent terms with his neighbours, including an indenture of friendship in 1467 with William, Lord Forbes and Rose of Kilravock.
Two years later another band of was executed between Duncan Mackintosh and Kilravock in which all debates would be referred to George Gordon, 2nd Earl of Huntly.
It is recorded in the Genealogical Deduction of the Family of Kilravock which was written 1683–4, that the Mackintoshes were ejected and that a royal summons was made against Donald.