Oxide perovskite materials with ABO(3) structure have been widely employed for photocatalytic applications. However, owing to the disadvantageous electron-hole recombination process and wide bandgap of some materials, the photocatalytic performance is seemingly restricted. Coupling two catalysts together through the formation of a heterojunction ensures effective charge carrier separation. The intimate interaction between the materials is propitiously useful for charge transfer, thereby increasing the efficacy. In this study, the photocatalytic activity of a KxNa(1-x)NbO3-BaBiO3 (KNN-BBO) heterojunction material for the degradation of Rhodamine 6G organic dye was investigated. The materials were extensively characterized by X-ray diffraction, UV-Vis diffused reflectance spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and N-2 adsorption isotherms. The degradation efficiency of the organic contaminant under 1 sun simulated sunlight is monitored by spectral analysis from UV-Vis absorption spectroscopy. The resistance to charge transfer was also observed by electrochemical impedance spectroscopy. The effect of the sintering temperature on the photoinduced degradation activity was also included in our study. An unsintered KNN-BBO (UKB) composite material is found to be the most efficient catalyst with 84% removal efficiency as compared to the sintered one (SKB). This is attributed to the reduced bandgap with staggered-type band alignment, increased surface area, and surface oxygen vacancy states. Together with the crucial findings of this work, a probable mechanism for enhanced photocatalytic activity has been proposed here.