<p>To address the issues in traditional hydrometallurgy that require oxidants for treating nickel-iron alloy and reductants for treating spent ternary cathode materials, this paper proposes a synergistic leaching process for nickel-iron alloy and spent ternary cathode materials in a sulfuric acid medium. The process utilizes metallic Ni, Fe, and Co in the alloy, as well as impurities Al and Cu in the ternary cathode materials, as in-situ reductants to reduce high-valence Ni (III), Co(III), and Mn(IV) to divalent soluble ions, while the alloy itself is oxidized to divalent ions and dissolved, thereby completely avoiding the use of external oxidants and reductants. Thermodynamic calculations reveal the reduction priority order as: Al &gt; Fe(0) &gt; Co &gt; Ni &gt; Fe(II) &gt; Cu. Kinetic analysis confirms that the leaching process is controlled by external diffusion (<i>R</i>² &gt; 0.91), and the apparent activation energies of Li, Co, Mn, Ni, and Fe range from 12.19 to 17.06 kJ/mol. Under optimal conditions (nickel – iron alloy dosage at its theoretical amount, liquid-to-solid ratio of 15 mL/g, sulfuric acid dosage at twice its theoretical amount, temperature of 85 °C, and time of 120 min), the leaching efficiencies of all target metals exceed 98%. This study provides a green, efficient, and potentially applicable new strategy for the synergistic recovery of nickel – iron alloy and spent ternary cathode materials.</p>