The transformation of agricultural waste into high-performance catalytic materials represents a promising route toward sustainable energy production. This study investigates the synthesis, structural characterization, and catalytic evaluation of lithium-impregnated silica derived from corn cob ash for biodiesel production. The silica was extracted through calcination and acid leaching, then impregnated with LiOH and calcined at 350 °C, 450 °C, 550 °C, and 650 °C. Comprehensive analyses using FTIR, XRD, SEM–EDS, and GC–MS confirmed the formation of Si–O–Li bonds and lithium silicate phases with optimal surface morphology. The catalyst calcined at 550 °C exhibited the highest biodiesel yield of 85%, attributed to a Li₂O content of 17.90% and a structurally balanced amorphous-crystalline framework. The RBD palm oil feedstock showed ideal conditions (FFA: 0.15%; moisture: 0.07%), and the triglyceride profile supported efficient base-catalyzed transesterification. Compared to traditional CaO or homogeneous alkali systems, the lithium-modified catalyst demonstrated superior reusability, stability, and reduced leaching. This work exemplifies how circular economy strategies can be integrated into catalyst design by valorizing biomass into functional materials for green fuel technologies.