The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is the world’s only freshwater porpoise and is endemic to the Yangtze River. However, it is now Critically Endangered, with its long-term survival very uncertain due to escalating anthropogenic pressure. Recent census data indicate an accelerating rate of decline, meaning that the time remaining in which to save this endemic porpoise may be shorter than previously anticipated. In this study, we used VORTEX models to project population trends and estimate the time to extinction (TE) for wild Yangtze finless porpoise populations in the Yangtze River, Dongting Lake and Poyang Lake, and for the “semi-natural” porpoise population in the Tian’e-Zhou oxbow reserve, using the most recent available baseline population data. The median predicted TE was 25–33 years in the Yangtze River and 37–49 years overall in the wild at the current rate of decline. However, the actual TE is very likely to be shorter than this estimate. For the Tian’e-Zhou population, the VORTEX model predicted a provisional increase in the number of porpoises, but a high extinction risk with increasing inbreeding depression. These findings highlight the very narrow time window within which effective conservation measures need to be undertaken. We address the need to establish a network of “reintroduction refuges” to preserve as many porpoise individuals as possible through coordinated translocations. Actions to restore the movement of porpoises between the main Yangtze channel and its appended lakes, reduction of mortality rates in lake habitats, and restoration of ecosystem function in the Yangtze River should also be implemented with a catchment-wide perspective.