In this study, a flower-like SnIn4S8/SmVO4 heterostructure was synthesized by applying a hydrothermal approach and used as a visible-light-driven photocatalyst to remove hexavalent chromium (Cr6+) and Rhodamine B (RhB). The process design and optimization were carried out by response surface methodology (RSM). An artificial neural network (ANN) was also used to determine the relative importance of operational factors. Under RSM-based optimal conditions, the Cr6+ and RhB removal efficiency reached 90.93 and 97.57%, respectively. Process modeling by ANN revealed pH as the most influential factor in Cr6+ and dye removal. The predominant photocatalytic activity of SnIn4S8/SmVO4 was attributed to its Z-scheme structure, leading to the significant separation of charge carriers and conserving the redox capacity of the photogenerated electron-holes. Kinetic studies revealed that the SnIn4S8/SmVO4 could achieve considerable rate constants of 0.036 and 0.080 min−1 to remove Cr6+ and RhB, respectively. Furthermore, the catalyst’s reusability was confirmed under optimal conditions.