Microbiologically influenced corrosion (MIC) is a major challenge for extending the service life of X65 pipeline steel, especially in environments with high concentrations of Pseudomonas aeruginosa. This study prepared a Ni-P/PDMS-SiO₂ hierarchical composite coating to extend protection by creating a dual-barrier defense system. Systematic electrochemical tests over 45 days showed that both bare X65 steel and the single Ni-P intermediate layer deteriorated rapidly. However, the composite coating maintained a relatively high level of low-frequency impedance modulus (|Z|_0.01 Hz), approximately 10¹⁰ Ω∙cm². It was six orders of magnitude greater than that of bare steel and did not show any significant change after being immersed in the P. aeruginosa-containing medium. Based on these results, it could be assumed that a stable Cassie-Baxter air plastron and a dense amorphous Ni-P interlayer have a combined effect of physically blocking bacterial attachment and metabolite infiltration, thereby providing a support structure. This paper offers a feasible approach to designing extended-life anti-MIC coatings in bacterial-laden environments.