John of Islay (or John MacDonald) (1434–1503) is a late medieval Scottish magnate.

He is Earl of Ross and the 4th Lord of the Isles as well as being Mac Domhnaill, chief of Clan Donald.

John, however, proves to be the last of the Lords of the Isles, overmighty subjects of the Stewart Kings of Scotland and virtual kings in their own right in the Western Isles.

His struggle for power with King James III of Scotland ends in humiliation, following which his illegitimate son Angus Óg rebls against his rule.

In a bitter civil war, John's fleet of galleys meets those of Angus sometime in the early 1480s off the coast of Mull at the Battle of Bloody Bay, in which John's cause is defeated.

After Bloody Bay he becomes an inconsequential figure; and Angus continues to dominate the affairs of Clan Donald up until his murder in 1490.

In 1493 James IV brings the Lordship of the Isles to an end.

John dies unlamented in 1503, having witnessed the almost complete destruction of his family inheritance.