An abundant and sustainable resource, lignocellulosic biomass (LB) offers great potential for the production of value-added chemicals and biofuel. However, a proper enzymatic hydrolysis is limited by the LB's intricate, and complex structure. Environmental and financial concerns are raised by the use of harmful substances, extreme temperatures, and large energy inputs in conventional pretreatment procedures. A sustainable substitute for LB pretreatment, deep eutectic solvents (DES), which were first proposed as green solvents, combine efficient lignin and hemicellulose breakdown with low toxicity and a less environmental impact. This chapter covers the properties, mechanisms, and effectiveness of DES in biomass breakdown, emphasising how it helps to get over LB's structure resistance. Along with the benefits of incorporating DES with other pretreatment methods like mechanical refining and microwave irradiation, important factors affecting DES pretreatment are explained, such as temperature, composition, biomass loading, and reaction time. DES is a promising option for sustainable biorefinery applications owing to its capacity to promote enzymatic hydrolysis and increase sugar yields. Considering its benefits, DES recycling techniques that are more cost-effective, scalable, and optimised are still essential for wider industrial use.