Typically, savannas experience frequent fires, which limit tree cover and promote flammable grass accumulation, whereas forests form dense canopies that exclude fires by reducing C4-grass fuel loads and creating a humid microclimate. However, extreme fires occasionally burn into forests. Although these are known to kill forest trees and can make repeat fires more likely, the long-term consequences of an extreme fire event for forest structure and potential forest savannization remain largely unknown. Here, we analysed whether an extreme fire event could, alone, alter forest species composition, vegetation structure, and fire regimes, or whether successive fires after an initial extreme fire event were necessary to trigger a biome transition. We found that forests that only burned once recovered, whereas those that burned again following an initial extreme fire event underwent a transition from closed-canopy forests to open, grassy systems. Our results suggest that, while extreme fires set the stage for a biome transition, subsequent fires are necessary for flammable grasses to colonise and establish, ultimately resulting in a savanna fire regime.