Up to date, the most common reactive intermediate for water reduction is metal hydride. The PyH^• intermediate proposed and manifested in this work offers a new perspective for the mechanism understanding of known photocatalytic systems and the design of new photocatalysts. The PyH^• intermediate is generated from the pyridine reaction centers via the light-induced PCET process, which is directly involved for the subsequent H–H bond formation via the hemolytic elimination of two PyH^• units. Recent theoretical investigations suggest that pyridinic nitrogen atoms of π-conjugated polymers may also act as the hydrogen-adsorbing sites for hydrogen evolution. It is of great interest to investigate that whether similar heterocycle-hydrogen radical intermediate is generated and involved in the water reduction catalyzed by carbon nitride and COF materials. The clarification of the reaction site and mechanism of these photocatalysts will be of great insignificance for the development of next-generation simpler, greener, and low-cost photocatalysts.