The soil organic matter (SOM) is searched for the biomarkers and specific features associated with the effect of wildfires by the case study of peat soil, Rheic Hemic Histosol (Lignic), in the south of the middle taiga of the Komi Republic. It is shown that fires considerably influence the peat organic matter. Pyrogenic activity is assessed according to the content of charcoal particles. SOM is examined using solid-state 13C-NMR spectroscopy to determine the concentrations of polycyclic aromatic hydrocarbons (PAHs) and benzene polycarboxylic acids (BPCAs). The used methods allow for diagnosing the effects of wildfires on the SOM composition. In the horizons with the signs of pyrogenesis, the share of carbon represented by aromatic fragments increases as well as the PAH concentration, mainly at the expense of naphthalene, phenanthrene, and chrysene. The carbon stock of pyrogenically modified compounds, amounting to 4.4 kg/m2, is for the first time assessed in the European north based on the BPCA content. The characteristics of pyrogenically changed organic compounds and their fragments obtained by different methods correlate well: the Pearson coefficient for the correlation of the carbon content in aromatic compounds (Caryl) with total BPCA content is R = 0.84 (p < 0.05) and with individual BPCAs, R = 0.81–0.90 (p < 0.05).