This distinguished family have been in Wigtownshire and Galloway since the fourteenth century. The origin of the name is disputed although there are two main theories.

The first asserts that the name is of Norman ancestry from the Barony d'Agneaux. This origin has the family moving from Normandy to England then on to Ulster then finally to Scotland.

The second possible origin of the name is a Celtic one through the native Ulster sept of O'Gnimh (pronounced O'New). The O'Gnimh were the hereditary Bards to the great O'Neils of Clan Aodha Bhuidhe in Antrim. The name went through many transformations, O'Gnive, O'Gnyw, MacGnive, finally being anglicized to Agnew. This would give the Agnews a common descent with other great names such as MacDonald and MacDougall through Somerled, the twelfth century King of the Isles.