Cu2O@Ag polyhedral core–shell nanoparticles with different morphologies (rhombicuboctahedral, cuboctahedral, truncated octahedral, and octahedral) have been successfully synthesized by a thermal decomposition approach. The Cu2O@Ag polyhedral core–shell nanoparticles were characterized by X‐ray diffraction, electron microscopy, surface‐area analysis, and diffuse reflectance spectroscopy. The XRD results confirm the presence of Cu2O and silver in the Cu2O@Ag samples. Electron microscopy studies prove the formation of a shell of silver nanoparticles on the polyhedral Cu2O microcrystals. The diffuse reflectance spectra of the Cu2O@Ag polyhedral core–shell nanoparticles show band‐gap absorption owing to Cu2O as well as surface plasmon resonance owing to silver nanoparticles. The catalytic activities of the Cu2O@Ag polyhedral core–shell nanoparticles were explored for the reductions of 4‐nitrophenol and methylene blue in aqueous solutions. The Cu2O@Ag core–shell nanoparticles with octahedral morphology show higher catalytic activity than the other Cu2O@Ag samples. The core–shell nanoparticles show a higher turnover frequency (TOF) and activity parameter (kact) for 4‐nitrophenol reduction and a higher apparent rate constant (kapp) for methylene blue reduction compared to the previously reported values. The reusability of the Cu2O@Ag polyhedral core–shell nanoparticles was also tested, and they show stability for up to five cycles without loss of efficiency.