The transition to renewable energy systems necessitates efficient strategies for valorizing lignocellulosic biomass (LCB), one of the most underutilized and abundant resources. Anaerobic digestion (AD) of LCB for biomethane generation is hindered by the recalcitrance of lignin, hemicellulose, and cellulose, necessitating the development of effective pretreatment methods. Deep eutectic solvents (DES) have emerged as effective alternatives to conventional pretreatment methods due to their tunable physicochemical properties and potential for selective lignin removal. DES pretreatment is highly effective in disrupting lignocellulosic networks by selectively removing hemicellulose and lignin while preserving cellulose, thereby enhancing enzymatic hydrolysis and biomethane yield. Among various formulations, Choline chloride-based DES combined with organic acids has shown superior lignin solubilization and improved AD performance across diverse biomass feedstocks. Critical analysis shows that acidic DES formulations generally achieve higher delignification than neutral systems. Furthermore, synergistic integration of DES with advanced techniques has the potential to reduce overall energy consumption and improve process efficiency. This review critically evaluates the role of DES-based pretreatments in the enhancement of biomethane production from LCB, by giving emphasis on the mechanism behind pretreatment, biomethane performance, integrated pretreatment approaches, and future prospects. Future research directions include elucidating molecular-level DES–biomass interactions and applying computational and machine-learning tools for rational solvent design to establish industrial feasibility. Overall, DES pretreatment represents a transformative and eco-friendly approach for enhancing biomethane generation from LCB.