With increased interest in the biodegradation of lignin, there is a pressing need to evaluate the feasibility of using microorganisms for lignin degradation. A novel Bacillus strain was separated from compost and identified as Brevibacillus thermoruber. B. thermoruber showed excellent performance in lignin degradation and degraded 81.97% of lignin after 7 d, which was similar to the lignin degradation rate of fungi. The biodegradation of lignin G and H monomers mainly proceeded via the β-ketoadipate pathway at 37 °C. At 55 °C, the degradation product of lignin S monomer was mainly a benzoic acid substance, indicating that the lignin was degraded via the benzoic acid pathway. The degradation products of lignin are important precursors for humus formation in compost. The results of this study provide new insights into the biodegradation pathway of lignin in different stages of composting.