West Pacific leatherback turtles nest in Indonesia, Papua New Guinea, the Solomon Islands and Vanuatu. They migrate and forage throughout Australian waters including Victoria. Since 2018 there has been an increase in bycatch of leatherbacks in Australia and New Zealand. Here we employed Population Viability Analysis (PVA) to examine leatherback population persistence under various bycatch scenarios. Our models predict a declining growth rate (λ = 0.987), a significant reduction in population survival probability (-28%) and a large reduction in adult population size (780 to 59) over the next ten generations even under pre-2018 bycatch conditions. Minimal additional mortality from bycatch (2 adults per year), such as seen since 2018, greatly exacerbates the risk of extirpation (by approximately 40%). The small Solomon Islands subpopulation is predicted to be extirpated by 2062 under pre-2018 bycatch conditions, with additional mortality accelerating the timeline to extirpation by 25 years. Unknown post-release survival rates and limited understanding of other fisheries-related impacts add further uncertainty regarding the resilience of West Pacific leatherbacks to bycatch. Both bycatch reduction and enhanced research on post-release survival should be prioritised to ensure that Australia and New Zealand contribute to preventing the extirpation of the Critically Endangered West Pacific leatherback population.