Pleurotus species include edible mushrooms that can grow on a broad range of lignocellulosic substrates by secreting a coordinated system of hydrolytic and oxidative enzymes. This flexibility offers opportunities to valorize agro-industrial residues for production of food and biomaterials using sustainable processes. In this study, we analyzed the genome of Pleurotus pulmonarius LGAM 28684 and investigated its biocatalytic potential for saccharification of pretreated lignocellulose using LC-MS/MS proteomics and biochemical assays. The fungus was cultivated on two lignocellulosic substrates, beechwood and corn stover, as well as xylose as a control. The fungus was cultivated on beechwood, corn stover, and xylose. Beechwood induced the richest secretome with abundant oxidases. The corn stover secretome had fewer proteins but was focused on carbohydrate-acting enzymes, with abundant polysaccharide-degrading and accessory enzymes. Despite lower enzyme diversity, the corn stover secretome achieved higher lignocellulose saccharification, further improved by oxidoreductase inhibition. Supplementing an industrial cellulase cocktail with P. pulmonarius corn stover secretomes enhanced sugar release by 40%. These findings highlight the dynamic enzymatic response of P. pulmonarius to lignocellulosic substrates and its potential in biomass valorization and the design of enzymatic cocktails.