Marine species are declining at an unprecedented rate, catalyzing many nations to adopt conservation and management targets within their jurisdictions. However, marine species are naive to international borders and an understanding of cross-border species distributions is important for informing high-level conservation strategies, such as bilateral or regional agreements. Here, we examined 28,252 distribution maps to determine the number and locations of marine transboundary species. Over 90% of species have ranges spanning at least two jurisdictions, with 58% covering over ten jurisdictions. The highest concentrations of transboundary species are in the USA, Australia, and Indonesia. To effectively protect marine biodiversity, international governance mechanisms—particularly those related to the Convention on Biological Diversity, the Convention on Migratory Species, and Regional Seas Organizations—must be expanded to promote multinational conservation planning, and complimented by a holistic governance framework for biodiversity beyond national jurisdiction.