Abstract In₂S₃ (β-In₂S₃), semiconducting chalcogenide with desirable physicochemical properties, has fascinated researchers in photoelectrochemistry. Because of its wide band gap, In₂S₃ can utilize solar energy below 600 nm. However, rapid photogenerated electron–hole recombination and low quantum efficiency have limited the practical application of In₂S₃ in this field. In a two-step in situ hydrothermal process we introduced a narrow band gap semiconductor (ReS₂) below the In₂S₃ and constructed a direct Z-scheme heterostructure with nanoflower and honeycomb morphology. The formation of a direct Z-scheme heterostructure and coordination of the trap-like structure of the composite give a wider absorption range, higher migration and separation efficiency, and faster interfacial transfer speed than for pristine In₂S₃, and the photoelectrochemical performance is approximately three times better than that of pristine In₂S₃ at 1.23 V versus a reversible hydrogen electrode under sunlight. This method therefore provides a new prospect for optimizing the performance of In₂S₃ and applying the novel heterojunction.