Herein, a 2D/0D g-C₃N₄/Cu₂SnS₃ heterostructure is successfully constructed via the facile calcination method, and its application to photocatalytic CO₂ conversion is demonstrated for the first time. The fabricated g-C₃N₄/Cu₂SnS₃ nanocomposite is featured with its unique Cu-C and Cu-N dual chemical bond at the interface. The engineered g-C₃N₄/Cu₂SnS₃ nanocomposites record a superior CO production rate of 18.2 μmol∙g^-1∙h^-1 with an apparent quantum yield of 2.2% at 500 nm under illumination, which is the highest among g-C₃N₄/ternary metal sulfide photocatalysts to the best of our knowledge. This notable improvement is attributed to the effective incorporation of Cu₂SnS₃ NPs onto the surfaces of ultra-thin g-C₃N₄ and, the formation of Cu-N and Cu-C dual bonds at the interface. This helps not only the activation of interface defect-mediated Z-scheme conduction but also supplies highly reactive Cu sites in the Cu₂SnS₃ NPs for efficient photocatalytic CO₂ conversion.