The São Francisco basin (SFB) is the largest watershed in eastern tropical South America, encompassing vast areas of savannas, xeric vegetation, and tropical forests. Here, we present a 72,000 years of microcharcoal record, including number and area of microcharcoal particles, of the SFB based on a semi-automated microcharcoal quantification method of the marine sediment core M125-95-3 (Latitude: -10.945; Longitude: -36.2057). Microcharcoal was identified and quantified using an approach combining chemical treatment, Raman spectroscopy for dark-particle identification, slide-scanning, and image analysis. Our results show that enhanced fire activity was closely linked to the expansion of open savannas, modulated by changes in the precipitation regime that were likely driven by orbital- and millennial-scale variability. The most intense fire regime, between 32 and 22 ka, coincided with the maximum expansion of open C4-dominated vegetation likely due to enhanced precipitation seasonality associated with a low obliquity phase.