The development of highly efficient and robust photocatalysts has attracted great attention for solving the global energy crisis and environmental problems. Herein, we describe the synthesis of a p–n heterostructured photocatalyst, consisting of ZnO nanorod arrays (NRAs) decorated with BiOI nanoplates (NPs), by a facile solvothermal method. The product thus obtained shows high photoelectrochemical water splitting performance and enhanced photoelectrocatalytic activity for pollutant degradation under visible light irradiation. The p‐type BiOI NPs, with a narrow band gap, not only act as a sensitizer to absorb visible light and promote electron transfer to the n‐type ZnO NRAs, but also increase the contact area with organic pollutants. Meanwhile, ZnO NRAs provide a fast electron‐transfer channel, thus resulting in efficient separation of photoinduced electron–hole pairs. Such a p–n heterojunction nanocomposite could serve as a novel and promising catalyst in energy and environmental applications. Improved electron–hole separation: ZnO nanorod arrays have been decorated with BiOI nanoplates. The p–n heterojunction thus obtained plays a significant role in photoelectrocatalytic processes, where the BiOI nanoplates provide reaction sites for the degradation of organic pollutants, and the ZnO nanorods provide a fast transfer channel for electrons, which are ultimately transported to the counter electrode along an FTO substrate (see figure; FTO=fluorine‐doped tin oxide).