Wildfires generally result in biospheric recovery approximating the pre-disturbance state. However legacy carbon(C) gains and losses that have until now been overlooked in global-scale theory and modelling indicate that post-fire C gains through pyrogenic carbon (PyC) production, and losses via fire regime shifts, post-fire mortality, topsoil loss and inland water export, may be central to whether 20th century fires have imposed a net terrestrial C source or sink. Here, we integrate PyC production and soil accumulation into a global terrestrial model (ORCHIDEE-MICT) and estimate wildfire C-gains and losses over 1901-2010, quantifying the fire-C balance at global, regional and vegetation scales. Excluding the effect of PyC mineralisation, fires provide a land storage of +177 TgC yr-1 (63% PyC production), dominated by grasslands. The global balance is nuanced, with forest fires resulting in strong terrestrial net C loss:gain ratios (>-2:1) that are greatest in tropical regions (>-3:1). Frequent tropical grassland fires are responsible for the bulk of the land PyC sink and its environmental persistence, whose theoretical minimum mean residence time we quantify at 2760yrs. We highlight the dependency of the global fire-C balance on vegetation coverage and the potential role of preserving grasslands, particularly those in the tropics, in that regard.