The emergence of the fungal pathogen Batrachochytrium dendrobatidis (Bd), which causes the disease chytridiomycosis in amphibians, is implicated in the severe decline of up to 200 amphibian species globally, 113 of which may be extinct. In remnant populations of declined species, Bd persists and chytridiomycosis can cause substantial ongoing mortality. The emergence of novel pathogens is predicted to drive changes in host life-history, yet the effects of Bd on amphibian life-history have not been examined. Here, we show that Bd is associated with life-history changes in amphibians that can make them more vulnerable to climatic extremes. We focus on the endangered alpine tree frog, a species that is restricted to a small number of remnant populations in sub-alpine regions of south-eastern Australia. In diseased populations, very few adults survive between years. However, Bd prevalence is low in early life-history stages, resulting in high recruitment and population persistence. We compare longevity, and age and size at maturity between diseased and disease-free populations, and also with museum specimens collected prior to Bd emergence. We demonstrate that populations with Bd have a severely truncated age structure driven by very high rates of adult mortality. This truncated age structure means that in chytridiomycosis-challenged populations, individuals breed once, compared with non-diseased populations where individuals likely breed multiple times. Using a combination of empirical evidence and population models, we also show that chytridiomycosis is associated with earlier sexual maturity. We use population simulations to illustrate that these shifts in life-history greatly increase the risk of decline when populations are subject to variation in recruitment success caused by drought. Our results show that chytridiomycosis can drive major life-history shifts in its amphibian hosts and underline the potential utility of minimizing other sources of mortality to mitigate the threat posed by this deadly pathogen.