AbstractThe efficient utilization of near‐infrared (NIR) light for photocatalytic hydrogen generation is vitally important to both solar hydrogen energy and hydrogen medicine, but remains a challenge at present, owing to the strict requirement of the semiconductor for high NIR responsiveness, narrow bandgap, and suitable redox potentials. Here, an NIR‐active carbon/potassium‐doped red polymeric carbon nitride (RPCN) is achieved for by using a similar‐structure dopant as the melamine (C3H6N6) precursor with the solid KCl. The homogeneous and high incorporation of carbon and potassium remarkably narrows the bandgap of carbon nitride (1.7 eV) and endows RPCN with a high NIR‐photocatalytic activity for H2 evolution from water at the rate of 140 µmol h−1 g−1 under NIR irradiation (700 nm ≤ λ ≤ 780 nm), and the apparent quantum efficiency is high as 0.84% at 700 ± 10 nm (and 13% at 500 ± 10 nm). A proof‐of‐concept experiment on a tumor‐bearing mouse model verifies RPCN as being capable of intratumoral NIR‐photocatalytic hydrogen generation and simultaneous glutathione deprivation for safe and high‐efficacy drug‐free cancer therapy. The results shed light on designing efficient photocatalysts to capture the full spectrum of solar energy, and also pioneer a new pathway to develop NIR photocatalysts for hydrogen therapy of major diseases.