Intrinsic defects and structural properties are two main factors influencing the photocatalytic performance of carbon nitride (CN) materials. Here, photoactive porous CN rods are fabricated through the thermal condensation of melem-based hexagonal supramolecular assemblies. To overcome the poor solubility of melem, we exfoliate the bulk melem using hydrochloric acid. The latter allows good dispersibility of the monomer in an aqueous medium, leading to the formation of H-bond bridged supramolecular assembly with good regularity in both size and rod-like morphology. After thermal condensation, a well-ordered structure of porous CN rods with fewer defects due to the high thermal stability of the melem-based supramolecular assembly is obtained. The new CN materials have a high specific surface area, good light-harvesting properties, and enhanced charge separation and migration. The optimal CN material exhibits excellent photocatalytic activity and durability towards hydrogen evolution reaction (HER) and CO2 reduction reaction (CO2RR, with good selectivity).