An unprecedented synthesis of terpolymers from bioderived monomers and elemental sulfur in one-pot is described. In this approach, biosourced compounds, namely, vanilin and furfurylamine-based benzoxazine and ionones (and carvone), and a waste product of petroleum industry, sulfur, were reacted in one pot to produce an advanced thermoset. The inverse vulcanization of these compounds was monitored, and the properties of the obtained terpolymers were characterized via spectral and thermal characterization methods. Moreover, a potential use of the polymers as a Li-S battery cathode was demonstrated, and over 400 mAh/g capacity more than 100 of cycles were observed. Electrochemical impedance spectroscopy studies were used to gain more insight into the lithium storage mechanism before and after cycling.