In this study, graphitic carbon nitride (g-CN) nanosheets (CNns) were modified using polyaniline (PANI) codoped with an inorganic (hydrochloric acid, HCl) and an organic (phytic acid, PA) acid. Our results revealed that these samples exhibited extended visible-light absorption and a three-dimensional (3D) hierarchical structure with a large specific surface area. They also inhibited photoluminescence emission, reduced electrical resistance, and provided abundant free radicals, resulting in high photocatalytic performance. The PANI/g-CN sample demonstrated outstanding photocatalytic activity of a Cr(VI) removal capacity of 4.76 mg·min·g, which is the best record for the reduction of a 100 ppm KCrO solution. Moreover, g-CN coupled with PANI monotonically doped with HCl or PA did not demonstrate increased activity, suggesting that the codoping of HCl and PA plays a significant role in enhancing the performance. The improved photocatalytic activity of PANI/g-CN can be attributed to the interchain and intrachain doping of PA and HCl over PANI, respectively, to create a 3D connected network and synergistically increase the electrical conductivity. Therefore, new insights into g-CN coupled with PANI and codoped by HCl and PA may have excellent potential for the design of g-CN-based compounds for efficient photocatalytic reactions.