Porous graphitic carbon nitride with nitrogen vacancies (N–CN) has been successfully synthesized using a facile CaCO₃ template method. The porous structure contributed to the increased surface area of the obtained N–CN photocatalyst. The formed N_3C vacancies perturbed the localized electron distribution and tailored the electronic band structure, leading to an extended visible light response and the enhanced dissociation and transportation of photoexcited charge carriers. As a result, the as-prepared N–CN photocatalyst exhibited a 3.2-fold enhancement in the H₂ evolution rate in comparison with a bulk CN photocatalyst, which was attributed to the modified architecture and the presence of N_3C vacancies.