We report the synthesis and characterization of ultra-tough polylactide-based ionic nanocomposites via melt-blending of commercial polylactide (PLA), imidazolium-functionalized poly(ethylene glycol)-based polyurethane (im-PU) and surface-modified sulfonated silica nanoparticles (SiO2–SO3H) using extrusion techniques. The proximity of bulky pendant imidazolium cationic sites attached onto the highly functionalized polyurethane to the anionic sulfonate groups at the silica nanoparticle surface readily allow maximizing dynamic ionic interactions within the resulting PLA-based materials. This new design leads to a unique property profile that combines ultra-toughness (no break) and ductility (up to 150%), without critical loss of stiffness as well as improved thermal stability (up to 40 °C higher compared to neat PLA). In addition, we present a detailed mechanistic study aiming at elucidating the energy-dissipative toughening in these PLA/im-PU/SiO2–SO3H blends under quasi-static and high-speed loadings (ca. impact, tensile, 3-points bending). Relying on Small-Angle X-Ray Scattering (SAXS), creep and rheological measurements, a toughening mechanism is finally proposed to account for the impact behavior of the resulting ionic nanocomposites.