A bio‐based strategy was adopted to design high‐performance polybenzoxazine (PBZ) hybrid composites using sustainable monomers derived from cardanol and vanillin, in combination with furfuryl amine (CV‐fa) and lauryl amine (CV‐la). These systems were reinforced with 3‐glycidoxypropyltrimethoxysilane (GPTMS) functionalized bio‐silica (BS) to further boost their multifunctional properties. Among them, the CV‐fa‐based PBZ exhibited superior thermal stability with a 10% weight loss temperature ( T d 1 ) of 375°C and a char yield of 37.5%, which increased to 48.4% upon 20 wt.% BS incorporation. In contrast, the CV‐la system, while initially less thermally stable ( T d 1 = 337°C, char yield = 16.9%), demonstrated remarkable hydrophobic behavior and corrosion resistance due to its long aliphatic chain. The LOI values improved to 36.9% (CV‐fa/BS) and 32.5% (CV‐la/BS), suggesting excellent flame‐retardant behavior. Water contact angle values reached to 142° and 147°, respectively for CV‐fa/BS and CV‐la/BS, indicating enhanced moisture resistant properties. Notably, CV‐la/BS achieved > 98% oil–water separation efficiency over 10 cycles. Electrochemical studies indicated the high inhibition efficiencies of 95.45% for CV‐fa/BS and 98.7% for CV‐la/BS, confirming their outstanding corrosion resistance. These bio‐based PBZ/BS composites offer a promising, eco‐friendly solution for advanced flame‐retardant, water‐repellent, and anti‐corrosion coatings.