The use of graphitic carbon nitride (g-C3N4)-based catalysts in the upgrading of lignocellulosic biomass significantly contributes to the greener production of biofuels, polymer precursors, and building blocks. In recent years, several catalysts based on g-C3N4 have been developed and applied in both photocatalyzed and non-photocatalyzed (thermal) reactions. This Review provides an overview on the upgrading of lignocellulosic biomass deploying several compositions of g-C3N4-based catalysts.