<p>In this study, a novel multicationic spinel system Cd_0.6Mg_0.2Cu_0.2Co_2-xFe_xO₄ (<i>x</i> = 0, 0.5, 1.0, 1.5) was synthesized via a sol–gel method and systematically investigated for its structural, chemical, and dielectric properties. XRD and Rietveld refinement confirmed a single-phase cubic spinel structure across all compositions, while XPS and Raman spectroscopy revealed the evolution of Fe³⁺/Fe²⁺ and Co³⁺/Co²⁺ redox pairs with increasing Fe content, enabling tunable polaronic conduction. Dielectric analyses, including impedance, electric modulus, and AC conductivity, demonstrated thermally activated relaxation governed by small polaron hopping, with a progressive shift from overlapping large polaron tunneling (OLPT) to non-overlapping small polaron tunneling (NSPT) mechanisms. Fe substitution significantly enhanced dielectric response and conductivity, reducing activation energy and relaxation time. Additionally, thermistor parameters (<i>β</i>, TCR, <i>α</i>) indicated high thermal sensitivity and negative temperature coefficient behavior, suggesting potential for temperature sensing applications. These findings underscore the synergistic role of multicationic doping and Fe-mediated conduction in optimizing dielectric and thermoelectric performance in spinel ferrites.</p>