In order to establish the Kermadec–Rangitāhua Ocean Sanctuary, which will protect a large, unique, near-pristine section of New Zealand’s marine environment, an improved understanding of the marine biodiversity of this area is required. Over 150 cephalopod specimens were collected from the Kermadecs during a recent biodiversity survey, providing the first opportunity in over a century to directly assess locally occurring taxa. Specimens were morphologically identified and DNA barcoded. DNA sequences were analysed using the Barcode Index Number (BIN) system in the Barcode of Life Data System. This study nearly doubles the previously known cephalopod biodiversity of the Kermadecs, adding 28 species (bringing the total to 70), and reporting three cephalopod orders from this area for the first time. The BIN analysis highlighted several taxa that are badly in need of revision, including some supposedly monotypic genera that now appear to contain multiple species, and at least five species that may be new to science. The Kermadec region also hosts 34 cephalopod species not known to occur elsewhere in New Zealand waters. Most taxa reported herein are deep-sea species whose habitat is not protected by the existing marine reserve; we therefore strongly support the establishment of the proposed Sanctuary.