The primary challenge regarding solid polymer electrolytes (SPEs) is the development of materials with enhanced mechanical modulus without sacrificing ionic conductivity. Here, we demonstrate that when stiff/rigid polymer nanoparticles that are thermodynamically miscible with a polymer are utilized in a blend with a liquid electrolyte, the elastic modulus and the ionic conductivity of the resulting SPEs increase compared to the linear polymer blend analogues. In particular, when poly(methyl methacrylate), PMMA, nanoparticles, composed of high functionality star shaped PMMA, were added to low molecular weight poly(ethylene oxide), PEO, doped with bis(trifluoromethane)-sulfonamide (LiTFSI), the resulting SPEs exhibit 2 orders of magnitude higher conductivity and 1 order of magnitude higher mechanical strength compared to their linear analogues. In addition, the former remain solidlike over an extended temperature range. Key to their performance is the morphology that stems from the ability of the PMMA nanoparticles to disperse within the liquid electrolyte host, allowing for the formation of a highly interconnected network of pure liquid electrolyte that leads to high ionic conductivity (comparable to that of the neat PEO electrolyte). The present strategy offers tremendous potential for the design of all-polymer electrolytes with optimized mechanical properties and ionic conductivity over a wide temperature window for advanced electrochemical devices.