Flexible conductors play an indispensable role in fabricating foldable LED displays [1], conformable biosensors [2], soft energy storage devices [3,4], organic transistors [5] and smart textiles [6]. Efforts were thus invested to develop highly flexible and conductive composites [7] via the percolation of conductive nanofillers in polymers [8]. Current research is mainly focused on the composites filled with carbon nanotubes (CNTs) [9,10] and silver nanowires (AgNWs) [11,12]. Experimental techniques [11,13–۱۵], computer simulations [11,15–۱۹] and theoretical models [20–۲۲] were used to study the percolation of the composites filled with the nanofillers with very large length-to-diameter aspect ratio. Major issues discussed include the effects of inter-nanofiller van der Waals (vdW) interaction, the curviness and cross-sectional size of these slender nanofillers on the percolation threshold and electrical conductivity of the composites. In addition to these slender nanofillers, metal nanoparticles (NPs) with small aspect ratio around one were also used in the composites [23–۲۵]. A typical example is the gold NP (AuNP)-polymer composite [25] which exhibits an electrical conductivity (σeff > 104 S/cm), orders of magnitude higher than those with slender nanofillers [7]. A large elongation up to 484% and substantial piezo-resistive effect are also obtained [25]. These excellent properties offer a new avenue to a conformable strain/ stress sensor network able to detect the stress/strain distributions on curvilinear surfaces. In particular, some NPs [25] are found to be self-assembled via the vdW interaction to form slender chains/nanofillers. This may offer a new design with largely decreased percolation threshold but further enhanced electrical conductivity. Motivated by the properties of the AuNP-polymer composites and the potential of this new design the present work aims to explore the distinctive percolation behavior and properties of the novel NP chain-polymer composites, reveal its electron transfer mechanisms and identify the key factors controlling the percolation process. The emphasis of the present study was placed on the key factors that determine the percolation threshold and the conductivity of the composite at different stages. These factors include the conductivity, shape and size of NPs, and the electron tunneling energy barrier of the matrix, which were not discussed in detail in previous studies. The present work thus has brought in new insights into the percolation behavior and the underlying physics for the conductive nanocomposite.