Graphitic carbon nitride (g-C<inf>3</inf>N<inf>4</inf>) has been proven as a potential photocatalyst in the research arena of water remediation, energy harvesting and organic dye degradation etc. Even though, g-C<inf>3</inf>N<inf>4</inf> has profound properties viz. photochemical stability, intriguing electronic band structures, suitable light harvesting, and bandgap energy of 2.7 eV even it has significant drawbacks such as poor disparity, low surface area and high recombination rate of photogenerated electron-hole pairs that leads to reduced photocatalytic activity. However, these drawbacks could be overcome by compositing g-C<inf>3</inf>N<inf>4</inf> with sulfides, ferrites and other metal oxides which provides charge separation, increased surface area and better light absorption. This detailed review focuses on various synthesis methods of g-C<inf>3</inf>N<inf>4</inf>-based secondary/ternary nanocomposite and applications in the area of hydrogen evolution, organic pollutant degradation, oxygen evolution and CO<inf>2</inf> photoreduction. Alongside, this critical review also summarizes the recent literature that deals with the preparation of g-C<inf>3</inf>N<inf>4</inf>/polymer composites and their energy storage and environmental remediation applications. Hence, this review article would attract the broad range of readers working in the research space of g-C<inf>3</inf>N<inf>4</inf> based composite towards various applications. © 2024 Elsevier B.V., All rights reserved.