This article explores the processing of structural, thermal, and dielectric properties of polypropylene (PP) polymer nanocomposites modified with Ni0.9Zn0.1Fe2O4. The PP/Ni0.9Zn0.1Fe2O4 nanocomposites are manufactured by the melt-processing method using a Brabender Polyspeed B. The XRD and FTIR structural investigations assure good incorporation of Ni0.9Zn0.1Fe2O4 into the PP matrix. It should be noted that adding Ni0.9Zn0.1Fe2O4 NPs to the PP polymer matrix enhances the polymer’s thermal stability. Utilizing the Coats–Redfern model, kinetic thermodynamic parameters such as activation energy (Ea), enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG*) are deduced from TGA data. The dielectric results showed an increase in ε′ with the introduction of nanoparticles into the PP matrix. As the content of Ni0.9Zn0.1Fe2O4 NPs in these nanocomposite films increases, the loss tangent values decrease at higher frequencies while increasing at lower frequencies. The estimated εs and ε∞ of PP nanocomposites using Cole–Cole plots reveal an improvement when NPs are added to PP. We believe that the proposed work suggests a relevant step towards the practical application of PP/Ni0.9Zn0.1Fe2O4 nanocomposites.