A range of nanocomposites based on a polyethylene polymer and hexagonal boron nitride (hBN) filler has been explored in this study. The dielectric properties of the nanocomposites, which consisted of 2 wt %, 5 wt %, 10 wt %, 20 wt %, and 30 wt % of hBN, have been compared to the dielectric properties of the unfilled polyethylene blend. Scanning electron microscopy (SEM) revealed that the hBN was uniformly distributed in the polyethylene matrix, although large amounts of agglomerates were present in the nanocomposites containing more than 10 wt % of hBN. The incorporation of hBN into polyethylene resulted in a highly disordered morphology in comparison to the unfilled polyethylene, in which this effect was more pronounced with increasing hBN content. This is consistent with the increasing crystallisation temperature as the hBN content increases, as shown by differential scanning calorimetry (DSC), where the hBN acted as a highly effective nucleating due to the strong interactions between the polyethylene and the hBN. This strong interaction is again reflected in the thermal decomposition temperature which similarly increases with increasing hBN content. The study demonstrates the remarkable electrical properties of the prepared nanocomposites, where the breakdown strength monotonically increased as a function of hBN content, even with a very high 30 wt % of hBN. The improvement in electrical properties, even at high hBN concentrations, is contradictory to the reported results in the literature and are mainly attributed to the hydrophobic surface of the hBN particles.