Cellulose nanopaper is a strong lightweight material made from renewable resources with a wide range of potential applications, from membranes to electronic displays. Most studies on nanopaper target high mechanical strength which compromises ductility and toughness. Herein, we demonstrate the fabrication of highly ductile and tough cellulose nanopaper via mechanical fibrillation of hemicellulose-rich wood fibers and dispersion of the obtained cellulose nanofibrils (CNFs) in ionic liquid (IL)-water mixture. This treatment allows hemicelluloses swelling leading to dissociation of CNF bundles into highly disordered long flexible fibrils and formation of a nanonetwork as supported by Cryogenic Transmission Electron Microscopy (Cryo-TEM) imaging. Rheology of the suspensions shows a hundredfold increase in storage and loss moduli of CNF-IL-water suspensions as compared to their CNF-water counterparts. The nanopaper prepared by removing the IL-water shows a combination of large elongation up to 35 %, high strength 260 MPa and toughness as high as 51 MJ/m3 due to efficient interfibrillar slippage and energy dissipation in the highly disordered isotropic structure. This work provides a nanostructure-engineered strategy of making ductile and tough cellulose nanopaper.