In this study, plasmonic PDA@Au/CeO2 composites were produced by a self-assembled redox approach. The morphologies, chemical compositions, and optical properties of the composites were investigated. The obtained results showed that the immobilization of Au NPs with good localized surface plasmon resonance (LSPR) properties together with the formation of CeO2(shell)-Au(core) structure onto polydopamine nanoparticles (PDA NPs, as both reducing and stabilizing template) led to the production of active oxygen vacancies between valance and conduction bands as well as enhanced the visible light absorption of the catalyst. The plasmon sensitized photocurrent stability and photoluminescence behaviors clearly revealed the close Schottky contact between CeO2(shell) and Au(core) which led to the decrease in the band gap of composites. Therefore, the study of the photocatalytic mechanism of composites demonstrated that increased ECB value, reduced band gap, great photoresponsivity, plasmon assisted charge separation/transfer properties, and production of active oxygen vacancies provided a new heterogeneous photocatalyst with reasonable good reusability and stability for efficient decolorization of MB under visible LED light irradiation.