In this study, silicon carbide (SiC) nanostructures were successfully synthesized through a high-temperature carbothermal reduction process at 1800 °C and subsequently incorporated into a polyvinyl alcohol (PVA) matrix to fabricate SiC/PVA nanocomposites with varying SiC filler concentrations ranging from 1 to 10 wt%. Comprehensive characterization techniques were employed to investigate the structural, morphological, optical, and dielectric properties of these nanocomposites. X-ray diffraction (XRD) analysis confirmed the formation of the cubic 3C-SiC phase, with crystallite sizes estimated between 13.84 nm and 39.23 nm using Williamson–Hall and Debye–Scherrer methods, respectively. Scanning electron microscopy (SEM) revealed distinct nanowire morphology of the SiC fillers, which plays a crucial role in the overall composite performance. Raman spectroscopy indicated high crystallinity of the nanostructures, supported by an intensity ratio (I_TO/LO) of 1.32. Optical studies using UV-Vis spectroscopy demonstrated a clear decrease in both direct and indirect band gaps with increasing SiC content, correlating with reduced crystallite sizes and enhanced interaction with the polymer matrix. Fourier transform infrared (FTIR) and Raman analyses further confirmed strong interfacial bonding between the SiC nanowires and PVA. Dielectric measurements revealed enhanced dielectric constants at low frequencies and elevated temperatures, with the 7 wt% SiC/PVA nanocomposite showing optimal performance attributed to Maxwell–Wagner–Sillars polarization effects and superior filler dispersion. These findings highlight the potential of SiC/PVA nanocomposites in advanced applications such as supercapacitors and sensor devices.