The Gallowglass derive their name from the Gaelic, Gall Gaeil meaning 'foreign Gaels'. They were a mercenary warrior elite that originated amongst Gaelic-Norse clans residing in the Western Isles and Highlands of Scotland. They served Irish lords from as early as 1259. By 1512 there were reported to be around sixty groups operating throughout the country under the control of the Irish nobility.

Initially they were mercenaries but over time they settled and their ranks were filled by the native Irish. Their preferred weapons were the two handed Sparth axe and the claymore broadsword. For amour, they wore chain mail shirts over padded jackets and iron helmets. A gallowglass was usually accompanied by two squires who carried his spears and provisions. They began to arrive in Ireland in considerable numbers to bolster the resistance of the Irish lordships against the Anglo-Norman invasion.

In Spring they would plough their fields, plant their seeds then gather their arms and armour and sail to Ireland to offer their services to the highest bidder. When the summer season of fighting was over, they would collect their earnings and return to Scotland to harvest their crops. In time, they began to secure lands for their services. During the escalation in military conflict of the sixteenth century, the gallowglass were joined by native Irish mercenaries known as Bunadha and a new breed of Scottish mercenary called Redshanks. In spite of the increase in the use of firearms, Gallowglasses remained in demand well into the seventeenth century. Their clan names endure to this day in Ireland, prominent ones include: Gallogly, MacCabe, MacDonnnell, McDonald, MacDowell, MacRory, Sheehy and MacSweeney.