In the context of efficient conversion of CO2 to high-value carbonaceous fuels, the development of photocatalysts for CO2 reduction having high solar-to-fuel energy efficiency with exceptional selectivity and long-term stability is the prime requisite of current research. Herein, we reported a novel straddling band configuration based Cu2ZnSnS4/Pt-integrated g-C3N4 heterojunction photocatalyst for CO2 reduction to carbonaceous fuels. The heterojunction photocatalyst exhibited an enhanced CO2 reduction with an average CO/CH4 yield rates of 17.351/7.961 μmolg−1 h−1, which is ∼3.31 and ∼5.56 folds higher than pristine g-C3N4. The comprehensive analysis of heterojunction photocatalyst exhibited synergetic effects owing to higher surface area, efficient photon harvesting due to CZTS and multiple charge-transfer pathways together with Z-scheme charge transfer. Moreover, the localized surface-plasmon-resonance (LSPR) and electron sink function of Pt led to an efficient interfacial charge carrier separation, surface site activation for CO2 reduction and in the consequence of that enhanced the photocatalytic performance.