Thermosets and composites were fabricated from the epoxides of norbornane seed oils (linseed oil, soybean oil, high-oleic soybean oil, and non-modified seed oils). The epoxides were cured using a cationic initiator to mold thermosets. Thermosets were characterized for their curing behavior and T g by dynamic scanning calorimetry, crosslinking efficiency by Soxhlet extraction, and thermal stability by thermogravimetric analysis (TGA). Steric hindrance of the norbornylized seed oils had a perturbing effect on the extent of epoxidation. However, the higher ring strain energy of the norbornene moieties played a key role in epoxide curing, resulting in higher T g thermosets with higher crosslinking efficiency. To the epoxide system with the highest optimum balance of T g, crosslinking efficiency, and thermal stability, lignocellulosic sorghum-derived biomass fillers were added. The addition of biomass fillers increased the bio-based content and reduced the cost and weight of the composites. Further, torrefied and carbonized sorghum filler variants were used to study the effect of the extent of thermal treatment on curing and on the final thermoset properties. Fillers were characterized by TGA, IR, elemental analysis, and solid-state NMR. Glass fiber-reinforced composites were molded using the optimum formulation. The mechanical and thermal properties of the novel hybrid biocomposites were investigated using universal testing machine (UTM), impact tester, and TGA. Both the sorghum-filled thermosets and composites showed enhanced thermomechanical property as compared to the non-filled epoxy systems. Carbonized sorghum filler composites exhibited the highest mechanical properties and thermal stability. Elemental differences and biomass precursor differences such as the cellulose, hemicellulose, and lignin content were found to play a critical role toward the composite properties. The SEM images showed good interfacial adhesion between the polymer matrix, fillers, and fiber phase in the biomass-filled composites. Thus, the fabricated composites demonstrate the potential for being used as sustainable, greener, and lightweight composites.