Biomineralization offers a sustainable strategy for protecting marine infrastructure; however, the lack of standardized criteria for selecting mineralizing microorganisms hinders the transition from laboratory to application. Herein, we report the in situ fabrication of a multifunctional biomineralized coating on steel, driven by a rationally designed marine Pseudoalteromonas consortium (LLA). By elucidating the biofilm-to-mineral transformation, we established a definitive screening framework delineating three critical prerequisites: (1) rapid formation of dense biofilms for early-stage protection; (2) metabolic generation of an alkaline microenvironment; and (3) abundant anionic functional groups in extracellular polymeric substances (EPS) to serve as nucleation templates. Guided by these criteria, the synergistic LLA induced the growth of a dense, polycrystalline calcite coating (∼ 22 µm thick) with low porosity (< 2%). This coating exhibits integrated multifunctionality: superior corrosion resistance, reducing corrosion rates by > 95% while withstanding 500 h of neutral salt spray and 150 h of acetic acid salt spray exposure; robust anti-icing performance (freezing delay > 1100 s) attributed to the Gibbs-Thomson effect within nano-confined pores; and active self-healing, where metabolic re-mineralization autonomously repairs physical and electrochemical defects. This work bridges microbial ecology and materials engineering, offering a scalable, “living” material strategy for next-generation smart marine coatings.