An innovative p–n heterojunction Bi₂S₃/ZnCo₂O₄ composite was first fabricated via a two-step co-precipitation and hydrothermal method. By controlling the weight amount of Na₂S and Bi(NO₃)₃ precursor, different heterogeneous xBi₂S₃/ZnCo₂O₄ were synthesized (x = 0, 2, 6, 12, and 20). The p–n heterojunction Bi₂S₃/ZnCo₂O₄ was characterized by structural, optical, and photochemical properties and the photocatalyst decoloration of indigo carmine. Mott–Schottky plots proved a heterojunction formed between n-Bi₂S₃ and p-ZnCo₂O₄. Furthermore, the investigation of the photocurrent response indicated that the Bi₂S₃/ZnCo₂O₄ composite displayed an enhanced response, which was respectively 4.6 and 7.3 times (4.76 μA cm⁻²) greater than that of the pure Bi₂S₃ (1.02 μA cm⁻²) and ZnCo₂O₄ (0.65 μA cm⁻²). Especially the optimized p–n Bi₂S₃/ZnCo₂O₄ heterojunction with 12 wt% Bi₂S₃ showed the highest photocatalyst efficacy of 92.1% at 40 mg L⁻¹ solutions, a loading of 1.0 g L⁻¹, and a pH of 6 within 90 min of visible light illumination. These studies prove that p–n Bi₂S₃/ZnCo₂O₄ heterojunction photocatalysts can greatly boost their photocatalytic performance because the inner electric field enhances the process of separating photogenerated electron–hole pairs. Furthermore, this composite catalyst showed good stability and recyclability for environmental remediation.