This study reports on the effects of polymer-filler interactions, especially transcrystallization, on controlling the conductive network formation in polyamide 6 (PA6)/multi-walled carbon nanotubes (MWCNTs) composites. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) results show that MWCNTs acted as strong heterogeneous nucleating agents for PA6 crystals. Transmission election microscopy (TEM) confirmed the formation of a thick transcrystalline layer on the surfaces of the MWCNTs in PA6/MWCNT composites. Such an epitaxial growth induced by MWCNTs during melt processing was due to crystallographic matching of MWCNTs and PA6 crystal lattices. Consequently, electrical conductivity measurements showed that, the formation of the heterogeneously nucleated PA6 transcrystalline layers on the MWCNTs’ surfaces, disrupted direct contact between adjacent MWCNTs and delayed the insulating-to-conductive transition in PA6/MWCNTs composites. Thus, the electrical percolation threshold was observed at much higher MWCNT contents compared to the rheological percolation threshold. Interestingly, the current-voltage (I-V) characterisations showed that even at a high MWCNT content of 10 wt.%, electron tunnelling was the dominant electron conduction mechanism, signifying the lack of direct contact between the adjacent MWCNTs in the PA6/MWCNTs composites. The findings of this study help better understand and control the conductive network formation mechanisms in conductive polymer composites with semi-crystalline matrices.