AbstractExcess glycerol from biodiesel production can be sustainably converted into value‐added products like glycerol carbonate, for its use in polymers, solvents, and as ecofriendly alternative as green chemical in various chemical industries. This study aims to synthesize a catalyst optimized for the glycerol and dimethyl carbonate (DMC) conversion to enhance the yield of glycerol carbonate. This reaction not only avoids the use of hazardous chemicals but also proceeds under relatively mild conditions. The metal oxides of MgO, CaO, NiO, Li2O, and LiNO3 were compared for catalytic activity, and lithium oxide achieved the highest performance, with a glycerol conversion of 83.5 ± 1.0% and a glycerol carbonate yield of 77.5 ± 2.0%. Subsequently, lithium oxide was employed in conjunction with an activated carbon support derived from flax shive, synthesized through a microwave‐assisted method. Phosphoric acid concentration (55–75 wt.%) and heating time (4–16 min) were systematically varied to maximize the average pore diameter of the support. Activated carbon characterized by a Brunauer–Emmett–Teller (BET) surface area of 1373 m2/g and an average pore diameter of 3.29 nm was obtained under optimal conditions: 75 wt.% phosphoric acid concentration and a 4‐minute heating time. The results showcase the exceptional performance of lithium oxide when used in combination with activated carbon with providing 87.9 ± 2.4% glycerol carbonate yield. Characterization techniques such as thermal gravimetric analysis (TGA), BET surface area analysis, X‐ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FT‐IR) were employed, alongside gas chromatography (GC) and proximate and elemental analyses to comprehensively characterize the physicochemical properties of the catalysts and elucidate their correlation with catalytic performance.