Multiphase immiscible polymer blend systems have shown great potential to reduce the electrical percolation threshold for conductive applications. However, the material generally possesses poor mechanical properties since none of the polymer components can highly maintain the original bulk properties and also because coarse phase sizes are generally obtained due to the incompatible interfaces. In this work, we report on a new technique to fabricate multiple percolated polymer composites through nano-fibrillation of a completely wet ternary blend system composed of a matrix and two minor phases. After melt compounding, polyethylene terephthalate (PET) formed dispersed droplets fully encapsulated by a conductive poly (ether-block-amide) (PEBA) layer in the polypropylene (PP) matrix. PET/PEBA nanofibrils with core-shell structures and a typical diameter of 100-200 nm were then generated through melt-spinning of the PP/PEBA/PET blends. The transformation of complex PET/PEBA droplets into high-aspect-ratio core-shell nanofibrils significantly reduced the phase continuity percolation threshold, allowing for the development of PET/PEBA network structures at low composites in a PP matrix with well-preserved bulk properties. This results in a new type of multiphase polymer composite material with enhanced electrical and mechanical properties as compared to the traditional multiple percolated polymer blends.