Cellulose nanocrystals (CNCs) are widely studied as reinforcing fillers for poly­mers. In many cases the mechanical properties of polymer/CNC nanocomposites do not match the theo­retical predictions, arguably on account of CNC aggregation. This problem can be mitigated through the addition of a small amount of a judiciously selected poly­­me­ric dispersant that also serves as a binder among the CNCs. We show that the addition of 1-5% w/w poly(vinyl alcohol) (PVA) has a very sig­nificant im­pact on the mechanical pro­perties of poly(ethylene oxide-co-epi­chloro­­hy­drin)/CNC nano­­compo­sites. Remarkable improve­ments of the stiffness and strength were observed at a PVA content as low as 1% w/w, and the extent of reinforcement increased up to a PVA content of 5% w/w, where Young’s modulus, storage modulus, and strength increased by up to 5-fold vis à vis the PVA-free nano­compo­sites. Similar effects were observed for CNC nano­­compo­sites made with polyurethane or poly­(methyl acrylate) matrices, demon­stra­ting that the approach is broadly exploitable. Laser scan­ning micros­copy based resonance energy trans­fer experi­ments that involved nanocomposites made with CNCs and PVA that had been labelled with rhoda­­mine and fluores­­cein, respectively, confirmed that the enhanced mechanical properties of the three-component nanocomposites are indeed related to an improved dispersion of the CNCs.