The mono-digestion of sludge in biogas production has limitations due to its inefficient process. To overcome this issue, co-digestion with food waste at an optimal mixing ratio can be applied to enhance biogas production. Additionally, further optimization can be achieved by adding biochar, which acts as a stabilizer and increases the systems buffering capacity. This study investigates the role of biochar as a process stabilizer in biogas yield through the co-digestion of food waste and sewage sludge. The substrates consisted of food waste and sewage sludge mixed at a 4:1 ratio, with cow dung serving as the methanogenic bacteria inoculum in a 1:1 ratio. Fermentation was performed in an 11 L reactor at 38°C, pH 7±0.2, and an agitation speed of 80 rpm, with biochar added in varying amounts of 0 g/L, 0.5 g/L, and 1.5 g/L. Parameters analyzed included pH, m-alkalinity, total solids (TS), volatile solids (VS), total suspended solids (TSS), volatile suspended solids (VSS), chemical oxygen demand (COD), and biogas volume. Results showed that a biochar addition of 1.5 g/L achieved best performance compared to 0 g/L and 1 g/L, producing 3.19 L/gVS.day of biogas. The optimal composition of methane, carbon dioxide, and hydrogen sulfide was 76.00%, 23.13%, and 0.31% (v/v), respectively, with a final VS reduction of 12,000 mg/L. Biochar addition significantly improved process stability and biogas production, highlighting its potential to enhance efficiency and support sustainable industrial-scale waste management.