As a bioactive ceramic that closely mirrors the composition of natural bone, hydroxyapatite (HAP) has gained prominence as a coating material in biomedical applications. Despite its excellent biocompatibility, its poor mechanical strength, limited corrosion resistance, and poor interfacial stability hinder its direct application on load-bearing implants. However, most reported coating strategies have been limited to either mineral or polymer-based systems, thereby failing to achieve a comprehensive balance of mechanical strength, corrosion protection, and biofunctionality required for orthopedic implants. The current study focused on developing a novel mineralized HAP/κ-C/PAN composite coating on 316 L stainless steel (SS) via electrophoretic deposition. The HAP coating incorporated a biopolymer (kappa-carrageenan), a synthetic polymer (polyacrylonitrile), and two rare-earth nitrates to address the multifaceted requirements of orthopedic implants. While prior studies have focused on either mineral phases to enhance bioactivity and individual polymers to improve mechanical and corrosion properties, the present work integrates all three components into a unified system. Sm³ ⁺ substitution for Ca²⁺ in the HAP lattice was validated by X-ray photoelectron spectroscopy (XPS), owing to their similar ionic radii. The coatings of HAP, M-HAP, M-HAP/Biopolymer, and M-HAP/Biopolymer/Synthetic polymer were compared hierarchically to evaluate the synergistic contributions of each phase. The final composite coating (M-HAP/κ-C/PAN) exhibited superior corrosion resistance in simulated body fluid (SBF), with a lower corrosion current density (0.27 × 10⁻⁵ A/cm²) than the uncoated substrate. It also demonstrated improved surface hydrophilicity conducive to cell adhesion and robust mechanical performance, confirming its suitability for advanced orthopedic implant applications. © © 2025. Published by Elsevier Ltd.