Cellulose nanocrystals (CNCs) represent a fascinating class of biogenic nanomaterials in a wide range of sustainable materials applications. However, the production of CNCs from the cellulosic biomass remains a significant bottleneck. Probably more than 90% of the accounts on CNCs preparation relies on sulfuric acid hydrolysis, a method that has remained largely unchanged since its introduction nearly 70 years ago. While strong sulfuric acid effectively hydrolyzes the disordered regions of cellulose and introduces sulfate half-ester groups that impart colloidal stability, the narrow reaction window for concurrent hydrolysis and sulfation limits material tunability. Moreover, large water consumption and poor yields (normally between 20–50%) are problematic in industrial scale-up. In this contribution, we present an improved method for producing sulfated CNCs by integrating pressurized HCl gas-assisted hydrolysis of plant-based fibers, followed by a controlled sulfation under mild conditions. This efficient approach enables the consistent production of sulfated CNCs with tunable surface charges, while significantly reducing water consumption and achieving excellent yields (>82%). The control over the sulfation degree facilitates systematic investigation on the effect of charges on chiral nematic self-assembly. Moreover, the energy efficiency expands the commercial potential of CNCs-based materials.