The carboxylic platform via mixed culture anaerobic fermentation holds significant potential for biorefinery applications. However, effective and economical methanogenesis inhibition remains crucial for maximizing production efficiency. This study investigates the use of biomass tar, derived from the pyrolysis of rice husk, as a methanogenesis inhibitor to enhance the anaerobic fermentation of food waste and boost the production of reduced fatty acids. The experimental results demonstrated that adding 5.0 g/L of tar achieved the highest hydrogen production, reaching 65.0 mL/g VS. Furthermore, increasing tar concentrations led to higher yields of reduced and longer-chain fatty acids, with butyrate production peaking at 726.8 mg COD (chemical oxygen demand)/g VS (volatile solid) with 30.0 g/L tar, and caproate at 128.6 mg COD/g VS with 10.0 g/L tar. GC-MS analysis identified phenolic compounds and furan derivatives as the primary inhibitory agents, which gradually degraded during fermentation. Microbial community analysis revealed that the tar-based inhibitors effectively suppressed dominant methanogenic archaea, including Methanothrix, Methanobacterium, and Methanosarcina, while promoting the enrichment of chain-elongating bacteria such as Clostridium_sensu_stricto and Clostridium_IV. This study suggests that integrating biomass tar from pyrolysis with anaerobic fermentation can serve as a highly efficient biorefinery approach, fully utilizing diverse organic wastes for sustainable energy production.