Peatlands are important global carbon sinks but face increasing fire vulnerability under projected warmer and CO2-rich climate conditions. Past high-CO2 periods in Earth’s history serve as an important prospect to improve our understanding of fire regime changes and linked ecosystem responses. Here, we report wildfires in Late Cretaceous temperate rainforests and wetlands that existed only ~ 900 km away from the South Pole. Multiple proxy evidence from macro- and microcharcoal, polycyclic aromatic hydrocarbons, maceral analysis, inertinite reflectance and charcoal morphology document frequent, low-temperature surface fires. The fire regime changes closely coincide with a hydroseral succession (i.e., terrestrialisation) from swamp forests to the earliest known coal-forming Sphagnum-peat bog from southern high latitudes. Despite fundamental differences in atmospheric and floristic composition, fire and vegetation in 90-million-year-old Cretaceous forests and peatlands appear to have interacted in ways remarkably similar to modern ecosystems, with recurrent burning maintaining open vegetation structure and promoting peatland development. Our deep-time study establishes fire as an intrinsic driver of high-latitude wetland ecosystems and provides critical constraints on fire regime responses and ecosystem resilience under warm, elevated-CO₂ greenhouse conditions.