Abstract: The photocatalytic activity of catalysts depends on the energy-harvesting ability and the separation or transport of photogenerated carriers. The light absorption capacity of graphitic carbon nitride (g-C₃N₄)-based composites can be enhanced by adjusting the surface plasmon resonance (SPR) of noble metal nanoparticles (e.g., Cu, Au, and Pd) in the entire visible region. Adjustments can be carried out by varying the nanocomponents of the materials. The SPR of noble metals can enhance the local electromagnetic field and improve interband transition, and resonant energy transfer occurs from plasmonic dipoles to electron–hole pairs via near-field electromagnetic interactions. Thus, noble metals have emerged as relevant nanocomponents for g-C₃N₄ used in CO₂ photoreduction and water splitting. Herein, recent key advances in noble metals (either in single atom, cluster, or nanoparticle forms) and composite photocatalysts based on inorganic or organic nanocomponent-incorporated g-C₃N₄ nanosheets are systematically discussed, including the applications of these photocatalysts, which exhibit improved photoinduced charge mobility in CO₂ photoconversion and H₂ production. Issues related to the different types of multi-nanocomponent heterostructures (involving Schottky junctions, Z-/S-scheme heterostructures, noble metals, and additional semiconductor nanocomponents) and the adjustment of dimensionality of heterostructures (by incorporating noble metal nanoplates on g-C₃N₄ forming 2D/2D heterostructures) are explored. The current prospects and possible challenges of g-C₃N₄ composite photocatalysts incorporated with noble metals (e.g., Au, Pt, Pd, and Cu), particularly in water splitting, CO₂ reduction, pollution degradation, and chemical conversion applications, are summarized.