Abstract Designing an active catalyst and an in situ route for the decoration of single atoms (SA) on graphitic carbon nitride (C 3 N 4 ) toward efficient photocatalytic H 2 evolution reaction has been a wide area of focus. However, ultralow loading of SAs and miniaturizing of the catalyst with excess nitrogen for maximized photocatalytic H 2 production from water remains challenging. Herein, a simple novel method is demonstrated to fasten ultralow concentration of Pt atom (0.08 wt.%) on template‐based N‐rich C 3 N 4 (C 3 N 4.6 ) via thermal polymerization and acid leaching method to get a visible light irradiation‐based H 2 production rate of 64100 µmol g −1 h −1 , with an apparent quantum yield of 25.3%, and long‐term stability. The synthesis process involves initially attaching platinum complex to SBA‐15, thermal polymerization of dicyandiamide, and the formation of Pt SAs anchored on the surface of C 3 N 4.6 . Pt SAs are found to coordinate and interact with the N‐rich sites and alter the electronic structure of the C 3 N 4.6 . The atomically dispersed Pt species not only act as a sink for photoexcited electrons but also work as reduction sites to facilitate the faster water reduction kinetics on the surface than Pt NP decorated C 3 N 4 , highlighting the potential of ultralow‐loading Pt‐SACs in promoting sustainable H 2 production.