Niamh Whitfield is a leading authority on the metalwork of early Medieval Ireland and Scotland . Celtic metalwork of the seventh to twelfth centuries is extremely accomplished technically, and she has aimed at a thorough understanding of its manufacture. She has also been concerned to place Early Medieval Celtic design in its European context, and to analyse its relationship with Anglo-Saxon and continental work, as well as its debt to traditions which ultimately originated in the Classical world.

Dr Whitfield has written about subjects as diverse as the origins of the gold used in early Medieval Ireland and Scotland, the development of animal ornament and geometrical principles of design. Her archival studies have succeeded in identifying the find-spot of the celebrated 'Tara' brooch and in documenting panels of ornament which are now missing. In addition, she has explored early Irish texts for attitudes to jewellery and clothing, considered the brooch as an emblem of status, looked at how brooches were worn, and whether descriptions of clothing and accessories in an early Irish saga provide an accurate description of contemporary finery.