A novel oxygen‐doped graphitic carbon nitride (OCN) material was designed and synthesized via the hydrothermal‐calcination method with melamine and hydroperoxide as starting materials. The OCN material was utilized as a highly efficient solid metal‐free photocatalyst for the synthesis of 3‐arylquinoxalin‐2(1H)‐ones via the catalytic decomposition of aryl diazonium salts under blue light irradiation. Following this approach, various 3‐arylquinoxalin‐2(1H)‐one derivatives could be obtained in moderate to excellent yields with broad substrate scope under mild conditions. Also, the OCN solid photocatalyst shows good recyclability in the reaction, there was no appreciable loss in yields observed even after 5 cycles. This methodology offers a practical, mild, and metal‐free alternative to the preparation of 3‐arylquinoxalin‐2(1H)‐ones.