A study on structural, thermal, temperature-dependent electrical properties such as AC conductivity and dielectric properties of flexible conductive chlorinated natural rubber (Cl-NR) were carried out with various contents of nickel oxide (NiO) nanoparticles. The role of fillers on DC conductivity of the composites was correlated with different theoretical models. The FT-IR spectra showed the characteristic absorption band for nano-NiO in the rubber indicating the effective incorporation of nanoparticles in Cl-NR. Optical bandgap energy was observed minimum for 5 phr loaded composite. TGA result showed that the thermal stability increased with NiO content in the polymer matrix. The dielectric properties and AC electrical conductivity increased significantly with the temperatures and also with the addition of nanoparticles up to 5 phr loading. The activation energy of the electrical conductivity decreases with an increase in temperature for all the systems. The higher value of dielectric permittivity explained the electrode polarisations at low-frequency region. The skewed semi-circular arc in the Cole-Cole plot observed for all the samples explained the semiconducting behaviour of the nanocomposites. Space charge polarisation and relaxation dynamics of Cl-NR composites were explained based on modulus spectra. The McCullough model was found to be the most promising one to explain the DC conductivity of the system which emphasizes the importance of interfacial interaction at the boundary of filler and the rubber chain for the network formation. According to the results of this study, these samples can be used in highly durable flexible electronic devices such as conductive sensors, actuators and super-capacitors.