The fabrication of ordered assemblies of noble metal nanoparticles on two-dimensional sheets is very challenging. We report here a facile bottom-up self-assembly method for the formation of ordered assemblies of silver nanoparticles on carbon nitride sheets. The ultrasonication of aqueous graphitic carbon nitride quantum dots (g-CNQDs) in the presence of Ag⁺ ions produces a silver–carbon nitride (Ag–CN_x) composite. Ordered assemblies of monodispersed silver nanoparticles on thin carbon nitride sheets are produced by the evaporation of an aqueous solution of these silver–carbon nitride composites. On evaporation of this solution, two-dimensional sheets are formed as a result of the condensation of g-CNQDs on the solid substrate. On drying, the silver nanoparticles are located in the voids of the carbon nitride. A glassy carbon electrode modified with these silver nanoparticle–carbon nitride sheets can be used as a highly sensitive electrochemical non-enzymatic sensor for H₂O₂ and glucose. The lowest detection limits for H₂O₂ and glucose were 0.6 nM and 0.6 μM, respectively. In addition, the ON–OFF–ON fluorescence response of these g-CNQDs was used for the highly sensitive detection of Ag⁺ ions and cysteine in aqueous media. The detection limits for Ag⁺ ions and cysteine were 50 and 80 nM, respectively.