The origins of the Kirwan family go back to Heremon of the Milesians, 6th century B.C. conqueror of Ireland, who probably hailed from Spain. In Irish their name is Ciardubháin ('black').

They have a long history of eminent ecclesiastics, both Catholic and Protestant. As priests and soldiers they had close connections with Europe. Richard Kirwan of Cregg Castle, Galway, who was 6ft 4in. tall, was with Dillon's Regiment at Fontenoy. His fondness for duelling caused his dismissal from the French army, whereupon he transferred allegiance to the Austrian army. In the 18th century there were a number of Kirwan medical men in France. James Kirwan was a physician to the indolent Louis XV.

The Kirwans are also connected with the Bordeaux wine region in France. An English merchant, Sir John Collingwood, bought a chateau and vineyards here in 1751. His daughter married Mark Kirwan from Galway. He was beheaded in the French Revolution, but the family managed to hold onto the estates. From Chateau Kirwan in the Medoc comes the prestigious French wine which still bears their name.