AbstractGaidropsarus mauritanicus sp. nov. is described from one specimen collected using a grab sample from the Tanoûdêrt Canyon (ca. 20° N) off Mauritania at a depth of 595 m. The new species was further observed during eight remotely operated vehicle (ROV) dives along the Mauritanian slope southwards down to the Tiguent Coral Mound Complex (~17° N) in a bathymetric range between 613 and 416 m. It can be distinguished from congeners by a combination of characteristics, including large eyes (38.1% head length [HL]), large head (25.8% standard length [SL]), elongated pelvic fins (35.7% SL), low number of vertebrae (44), and coloration (pinkish with a dorsal darker brownish hue and bright blotches along the dorsal‐fin base). A species‐delimitation analysis performed with available cytochrome c oxidase subunit 1 (COI) sequences affiliated to the genus Gaidropsarus additionally supported the validity of the new species. Video analyses showed a deep‐water coral‐associated and protection‐seeking behavior, which may explain why the species has remained undescribed until now. Additional ROV footage from separate deep‐water coral sites in the North Atlantic and Mediterranean Sea further highlights the ecological behavior and hidden diversity of bathyal three‐bearded rocklings. Here, we additionally discuss the biogeographical distribution of all genetically verified Gaidropsarus spp. in combination with genetic data and morphological characters. G. mauritanicus sp. nov. is closely related to a species from Tasmania (43° S), a geographical point furthest among the studied samples, which may hint to an important influence of (paleo‐) oceanography on the distributions of Gaidropsarus species.