Climate change alters the frequency and intensity of wildfires, but its impact on the seasonal patterns of wildfires remains underexplored. Here, we quantify historical changes in wildfire seasonality across different ecoregions in North America and assess how climate change may affect these seasonal patterns. Our study finds that boreal and taiga forests have experienced a clear advance in seasonal wildfire activity, whereas Mediterranean and desert regions show delayed and extended late-season burning. Prairie and humid forest regions exhibit comparatively muted change. Attribution analysis shows that atmospheric dryness is the dominant control, while antecedent temperature, precipitation, and soil moisture indirectly shape wildfire risk through vegetation and fuel continuity at different lag times. These findings provide a basis for interpreting future region-specific changes in wildfire seasonality and emphasize the need for region-specific assessments of future wildfire activity. Plain Language Summary Wildfire seasons across North America are shifting in different ways as the climate changes. We combined satellite records, climate projections, and statistical models to examine how wildfire seasons have changed and how they may shift under future warming. Our analysis shows that wildfire seasons are moving earlier in northern forests, barely changing in grasslands, and shifting later in drought-prone western regions. These differences occur because each region responds differently to warming, drying, and changes in vegetation. Our findings highlight that wildfire risk will evolve in distinct ways across ecosystems, underscoring the need for region-specific planning and adaptation.