Anaerobic digestion is widely used for stabilizing waste activated sludge and recovering methane, but its efficiency is limited by the slow hydrolysis of complex organic matter. This study investigates a novel combined pretreatment approach using ascorbic acid (ASA) and ultrasonication (US) to enhance sludge solubilization and methane yield. The effectiveness of ASA, US, and their integration (ASA–US) was evaluated in terms of solubilized COD, biopolymer release, methane production, and microbial community shifts. The optimal combined pretreatment (0.04 g/g TSS ASA and 1.625 W/mL US) achieved 21.7 % COD solubilization—higher than ASA (7.6 %) and US (14.2 %) alone. Methane yield increased by 109.6 % compared to the control, reaching 285 ± 4 mL/g VS for ASA-US pretreated sludge. Kinetic modelling (Modified Gompertz and Logistic models) confirmed the enhanced biodegradability of the pretreated sludge. Microbial analysis revealed a notable enrichment of hydrolytic and acidogenic taxa such as Firmicutes and Clostridia, with a concurrent reduction in Proteobacteria, indicating a community shift favouring methanogenesis. Mechanistically, ASA promoted EPS disruption and deflocculation, while US-induced cavitation facilitated microbial cell lysis, collectively enhancing hydrolysis. These findings demonstrate that ASA–US pretreatment is an effective and synergistic strategy to improve methane recovery from waste activated sludge.