This study introduces the Peat Moisture Code (PMC), a component being integrated into the next-generation Fire Weather Index (FWI) System, designed to represent fuel moisture dynamics in ecosystems with deep organic soils (>40 cm). The PMC accounts for precipitation, evapotranspiration, and peat hydro-physical properties in a water balance model to estimate changes in storage and effective water table depth as a proxy for wildfire potential. Historical PMC values were calculated for nine areas with substantial peatland cover to evaluate their temporal variability and relationship with peatland burned area (PBA). The PMC exhibited distinct annual cycles, peaking in summer and reaching minimum values in winter (January). Mean annual PMC values ranged from 16.6 ± 14.2 at Matagami (QC; 1974–2024) to 49.4 ± 18.9 at Stony Rapids (SK; 1987–2024). Significant long-term (>30 years) increasing trends were observed at several western and northern sites (e.g., Norman Wells, Hay River), while some slight declining trends appeared when series were analyzed for the past 30 years (e.g., Big Trout Lake). Correlations between PMC and PBA were significant at multiple locations, with ρ = 0.31–0.60 (p < 0.05) for annual mean values and ρ = 0.34–0.61 (p < 0.05) for annual maximum values. Unlike the Drought Code (DC), the PMC showed stronger correlations with PBA, likely due to its sensitivity to peat moisture dynamics. Overall, this dataset provides benchmarks with the potential to be used in the development of peatland-type or region–specific fire danger thresholds for operational fire management and planning.