Indigenous land stewardship and mixed-severity fire regimes both encourage landscape heterogeneity and the relationship between them is an emerging area of research. To contribute to this exploration, we reconstructed the historical fire regime of Ne Sextsine, a 6000-ha dry, Douglas-fir-dominated forest in the traditional territory of the T’exelc (Williams Lake First Nation) in British Columbia. Between 1550 and 1982 CE, we found median fire intervals of 15 years at the plot-level and 4 years at the study site-level. Ne Sextsine was characterized by a historical mixed-severity fire regime, dominated by frequent, low-severity fires indicated by fire scars with infrequent, mixed-severity fires indicated by cohorts. Differentiating low- from mixed-severity plots was key to understanding the drivers of the fire regime at Ne Sextsine: high fire frequency in low-severity plots plateaued in the 1870s, following the smallpox epidemic, the forced relocation of Indigenous peoples into small reserves, and the prohibition of Indigenous burning. In contrast, high fire frequency in the mixed-severity plots continued until the 1920s when industrial-scale grazing and logging began. T’exelc oral histories and archaeological evidence at Ne Sextsine speak to varied land stewardship across the area, reflected in the spatiotemporal complexity of low- and mixed-severity fire. Across Ne Sextsine, 63% of cohorts established after the Indigenous fire regime collapsed, resulting in a dense, homogenous landscape that is more likely to burn at uncharacteristic high severities. This nuanced understanding of the Indigenous contribution to a mixed-severity fire regime is critical for advancing proactive fire mitigation that is eco-culturally relevant.