Rational design and development of photocatalytic materials is of paramount importance for efficient utilization of solar energy in photocatalytic applications. The conventional drawbacks of poor charge carrier separation and low light absorption of photocatalytic materials are the main issues that need to be addressed. However, the strategic combination of the formation of heterojunctions and plasmonic energy conversion is an effective solution to address these problems. In this work, Au nanostars (Au NST) were decorated over the surface of graphitic carbon nitride (GCN) and reduced graphene oxide (RGO) nanosheets and their catalytic potential towards polluted water remediation and organic reactions has been demonstrated under visible light illumination. The enhanced photocatalytic activity of the as synthesized photocatalysts towards both of these applications can be ascribed to the plasmonic effect of Au NST, efficient separation of the charge carriers and their improved transfer due to the formation of Au NST–GCN–RGO interfacial contacts. In addition, plausible mechanisms to explain the role of the photocatalyst for both of the applications have been proposed based on the obtained results. Overall, this work is expected to provide deeper physical insights into future development of plasmon-enhanced photocatalysts.