Display omitted •MnFe2O4-biochar enhanced the performance and stability of the AD of SS.•MnFe2O4-biochar addition led to 55.86% increase in cumulative methane yield.•MnFe2O4-biochar enhanced digestion performance via help establishing DIET.•MnFe2O4-biochar was helpful for immobilization and risk reduction of HMs in SS.•MnFe2O4-biochar treatment enhanced acetoclastic methanogenesis pathway. This study investigated the effects of MnFe2O4-biochar on sludge anaerobic digestion performance, methane production and heavy metal stabilization. The highest cumulative methane yield was achieved when the MnFe2O4-biochar dose was 1.50 g, which was 55.86% higher than control. A suitable dose of MnFe2O4-biochar stimulated methanogenic activities and improved methane yield, whereas excessive addition shows an inhibitory effect on anaerobic digestion. MnFe2O4-biochar addition significantly enhanced the biodegradation of organic matter, as the average volatile fatty acids degradation rate increased by 35.44%, compared to the control. Chemical speciation analyses demonstrated that MnFe2O4-biochar addition was more helpful for immobilization and risk reduction of heavy metals in sewage sludge. Simultaneously, microbial community analysis indicated that MnFe2O4-biochar obviously enriched acetoclastic methanogens Methanosarcina that capable of participating in direct interspecies electron transfer, which could accelerate substrate decomposition and methane production. These findings supply useful information for the resource utilization of sewage sludge.