The correct identification of the seabird species caught in fishing gear is of particular conservation concern. Northern Buller’s Albatross (Thalassarche bulleri platei) and Southern Buller’s Albatross (Thalassarche bulleri bulleri) are often bycaught by fishing vessels in New Zealand, but it has been difficult to determine the provenance of caught birds and identify species. We used a combination of mitochondrial DNA (mtDNA) and nuclear genome sequencing to assess the genetic differences between the Buller’s Albatross subspecies and whether there is suitable genetic marker for determining provenance. DNA was isolated from samples collected from 73 birds, which comprised of two Northern colonies (n = 26) and two Southern colonies (n = 47). DNA sequences from the mtDNA control region showed a high level of genetic differentiation between the Northern and Southern groups. All bycaught individuals could be assigned to their subspecies group. An analysis of molecular variance did not find any significant population structuring among the breeding colonies of each subspecies. A nuclear DNA set of single-nucleotide polymorphism (SNP) markers was obtained using a Genotyping-by-Sequencing (GBS) approach. We found 26 319 putative loci and 54 061 SNPs. A filtered-set of SNPs showed two distinct genetic clusters that corresponded to Northern and Southern Buller’s albatrosses, but there were limited fine-scale differences among colonies. The mtDNA and GBS data sets appear to produce similar findings.