Herein, we report, for the first time, sulfur-medidated synthesis of CTF-1 (S-CTF-1) using 1,4-dicyanobenzene and elemental sulfur without any catalysts or solvents. The formation of CTF engages in-situ vulcanization with elemental sulfur, enabling both covalent attachment of sulfur and its homogeneous distribution within the pores. S-CTF-1 was found to have a high sulfur content of 62 wt% along with a well-shaped bipyramidal morphology that has been achieved without using any external template. We have also examined electrochemical performance of S-CTF-1 as a sulfur-cathode material in Li-S batteries. S-CTF-1 exhibited robust cycling performance for 300 cycles with 85.8% capacity retention along with the highest initial Coulombic efficiency (ICE) reported to date: 94.4% at 0.05C (25 mA g-1). Our results demonstrate the promising aspect of microporous polymers as active supports for sulfur, thus it is expected to motivate further research in this area. In a broader perspective, direct utilization of elemental sulfur in the synthesis of covalent triazine frameworks can open up new high-value applications, such as advanced electrode materials for energy storage and conversion.