Photocatalytic reduction of CO2 is known as one of the most promising methods to produce valuable fuels and value-added compounds. To overcome selectivity and efficiency downsides, various photocatalysts have been designed and developed. This review discusses the state-of-the-art in photo-conversion of CO2 over graphitic carbon nitride (g-C3N4)-based composites. The modification strategies to improve photocatalytic activity of g-C3N4 were classified into different categories and discussed as structural modifications, elemental doping, copolymerization, fabricating heterojunctions between g-C3N4 and other semiconductors, Z-scheme heterojunctions, noble metal/g-C3N4 photocatalysts, and design of ternary nanocomposites based on g-C3N4. Finally, perspectives and future research works in this field were also outlined.