<p>The rapid expansion of high-frequency communication technologies, particularly in 5G and radar systems, has underscored the critical need for efficient electromagnetic interference (EMI) shielding in the K-band frequency range (18–26.5&#xa0;GHz). In this work, polyaniline/nickel ferrite (PANI/NF) nanocomposites were synthesized via in-situ chemical oxidative polymerization to address this challenge. The optimized composites exhibited an outstanding shielding effectiveness (<i>SE</i>) of 78.07 dB in the K-band, predominantly driven by absorption rather than reflection, a highly desirable trait for minimizing secondary radiation. <i>Green index</i> (<i>GI</i>) values exceeding unity and the reduced skin depth reveal the synergistic interaction between the conducting polymer (CP) matrix and magnetic ferrite filler, leading to enhanced attenuation and environmental compatibility. This material mutualism boosts the shielding efficiency and ensures sustainability, marking these composites as strong candidates for advanced EMI shielding applications. Notably, the shielding performance observed here ranks among the highest reported for PANI/ferrite systems in the K-band, while uniquely correlating <i>SE</i> with skin depth and <i>GI</i>, thus offering valuable insights for the development of next-generation green shielding materials for aerospace, telecommunications, and flexible electronics.</p>