The present study demonstrates the synthesis of an allyl-terminated imidazole cored trifunctional benzoxazine monomer and its subsequent hybridization with thiol-functionalized polyhedral oligomeric silsesquioxane (SH-POSS) through thiol-ene reaction, followed by the thermal ring-opening polymerization, leading to the formation of hybrid composites. The thermogravimetric analysis of the polybenzoxazine (poly(ITP-aa)) and its hybrid composites (poly(ITP-aa)/SH-POSS) indicates enhanced thermal stability along with a residual char yield of up to 56% for the poly(ITP-aa)/20 wt.% SH-POSS composite, evidencing the development of a densely cross-linked polymeric network. Electrochemical assessments conducted via electrochemical impedance testing and potentiodynamic polarization measurements demonstrate the superior barrier resistance of the coatings on mild steel (MS). The coating with 20 wt.% SH-POSS as reinforcement possesses the highest inhibition efficiency of about 99% in neutral medium. UV irradiation of the coatings at 365 nm for a period of 7 days shows only minimal changes in the values of absorbance along with a high optical transparency (> 95%), demonstrating the durability of the hybrid composite coatings. Further, the poly(ITP-aa)/20 wt.% SH-POSS composite system exhibits a WCA of ~139°, ascertaining its pronounced hydrophobic nature along with anti-icing, surface clean ability and oil–water separation characteristics suitable for advanced multifunctional coating applications.