For more than a century, discussions of Agnew origins were dominated by a handful of traditional theories. Many published accounts traced all Agnews to the Scottish Agnews of Lochnaw in Galloway, while others proposed Norman origins from the Barony of Agneaux in Normandy. In Ireland, historians also noted the existence of the Gaelic O’Gnimh (O’Gneeve) bardic family of County Antrim, hereditary poets to the O’Neills of Clandeboye, whose surname became anglicized as Agnew. Despite these competing explanations, it was commonly assumed that most or all Agnews shared a single paternal origin, particularly because they had temporal and geographic overlap in the Kilwaughter and Larne areas of County Antrim.

Modern genetic genealogy has revealed a more complex picture. Y-DNA testing within the Agnew Surname Project demonstrates that the surname has multiple independent paternal origins. Project participants currently fall into three principal haplogroups:

• I-M223: A traditionally Scottish Agnew lineage, including descendants associated with the historical Agnews of Lochnaw and the Channel Islands.
• R-M198: A distinct continental European lineage represented primarily by Agney and Agne families of Germanic origin.
• R-M269: An Irish Gaelic lineage associated with descendants of the O’Gnimh (O’Gneeve) family of County Antrim, whose surname was later anglicized to Agnew. Historical and documentary evidence places the O'Gneeves in County Antrim for centuries before the arrival of their Scottish counterparts from Lochnaw.

These discoveries show that the Agnew surname is not the product of a single paternal ancestry. Instead, it represents several historically distinct families who came to bear similar or identical surnames through different cultural, linguistic, and geographic pathways. By combining DNA analysis with documentary research, the Agnew Surname Project seeks to identify these separate origins and reconstruct the unique history of each Agnew family line.