Shifting fire regimes are causing widespread changes in the habitats of threatened species across southern Australia. Human activities have led to increased fire size, frequency, and severity in diverse ecosystems, threatening numerous animal species. This study used big data to analyze multidecadal changes in fire regimes from 1980 to 2021 in 415 reserves (21.5 million hectares) and 129 threatened species' ranges, including birds, mammals, reptiles, invertebrates, and frogs. The results show a decline in unburnt vegetation (≥30 years without fire) and an increase in recently burnt vegetation (≤5 years since fire) and fire frequency. The mean percentage of unburnt vegetation in reserves decreased from 61% to 36%, while the mean percentage of recently burnt vegetation increased from 20% to 35%, and fire frequency increased by 32%. These trends are primarily driven by the record-breaking 2019-2020 fire season. High-elevation species and reserves in the southeast of the continent experienced the most severe impacts. The study highlights the need for management strategies that conserve fire-threatened species in an increasingly fiery future. Altered fire regimes are having widespread ecological impacts, including carbon emissions, waterway pollution, and habitat destruction for threatened wildlife. Long-unburnt vegetation, crucial for many species, is decreasing due to increased fire frequency. The study underscores the importance of developing fire management approaches that protect vulnerable species in a changing climate.Shifting fire regimes are causing widespread changes in the habitats of threatened species across southern Australia. Human activities have led to increased fire size, frequency, and severity in diverse ecosystems, threatening numerous animal species. This study used big data to analyze multidecadal changes in fire regimes from 1980 to 2021 in 415 reserves (21.5 million hectares) and 129 threatened species' ranges, including birds, mammals, reptiles, invertebrates, and frogs. The results show a decline in unburnt vegetation (≥30 years without fire) and an increase in recently burnt vegetation (≤5 years since fire) and fire frequency. The mean percentage of unburnt vegetation in reserves decreased from 61% to 36%, while the mean percentage of recently burnt vegetation increased from 20% to 35%, and fire frequency increased by 32%. These trends are primarily driven by the record-breaking 2019-2020 fire season. High-elevation species and reserves in the southeast of the continent experienced the most severe impacts. The study highlights the need for management strategies that conserve fire-threatened species in an increasingly fiery future. Altered fire regimes are having widespread ecological impacts, including carbon emissions, waterway pollution, and habitat destruction for threatened wildlife. Long-unburnt vegetation, crucial for many species, is decreasing due to increased fire frequency. The study underscores the importance of developing fire management approaches that protect vulnerable species in a changing climate.