Lady Agnes Campbell (1526–1601) was the daughter of The 3rd Earl of Argyll and his wife, Lady Jean Gordon, daughter of The 3rd Earl of Huntly. She was probably born at Castle Campbell which was the Campbell Family seat. Her sister, Elizabeth, married The 1st Earl of Moray. Lord Moray was an illegitimate son of King James IV of Scots.
Lady Agnes married James MacDonald of Dunyvaig and the Glens in 1545, forming an alliance with the MacDonalds. They had a daughter named Fionnghuala, or more famously known as Ineen Dubh. Fionnghuala married Aodh mac Maghnusa Ó Domhnaill. James died in 1565 while he was being held prisoner by the Irish chieftain Shane O'Neill. Shane at that time had been supporting the English.
In 1569 Agnes went to Ireland to marry Turlough Luineach O'Neill who had replaced Shane O'Neill as the Chieftain of the O'Neill's in Ulster. She took with her a dowry of 1,200 Highland troops. Gaelic tradition allowed her to lead these troops herself. She led them against occupying English forces and proved herself to be a formidable leader. She helped mobilize Scottish support for the Irish and was fluent in English and Latin - which greatly impressed the English.