In pursuit of sustainable and high‐performance materials, bio‐based trifunctional benzoxazine monomers (VG‐Bz) were synthesized using eco‐friendly sustainable vanillin and guaiacol‐based trifunctional phenolic precursors with varied natures of primary amines, viz., aniline (a), furfuryl amine (fa), lauryl amine (la), and stearyl amine (sa), with paraformaldehyde through Mannich condensation reaction in the absence of solvent. The resulting benzoxazine monomers, VG‐a, VG‐fa, VG‐la, and VG‐sa, were thermally polymerized to obtain corresponding polybenzoxazines (PBZs) and comprehensively characterized for their curing behavior, thermal stability, flame retardancy, hydrophobicity, and corrosion resistance. Thermogravimetric analysis provides that poly(VG‐a) and poly(VG‐fa) exhibited superior thermal stability with high char yields, due to the presence of rigid aromatic structures. Data from water contact angle studies indicate that poly(VG‐sa) possesses enhanced hydrophobicity due to the presence of long alkyl chains compared to those of other samples of polybenzoxazines. An incorporation of GPTMS‐functionalized bio‐silica (BS) into the poly(VG‐sa) matrix further improved thermal resistance, water repellence, and anti‐corrosive properties. Electrochemical impedance spectroscopy (EIS) and Tafel polarization studies in 3.5 wt% NaCl solution confirmed the exceptional corrosion protection efficiency of poly(VG‐sa)/20% BS, achieving a maximum inhibition efficiency of 99%. These results highlight the potential of VG‐Bz systems, particularly the poly(VG‐sa)/BS hybrids, as environmentally benign coatings for advanced thermal and corrosion‐resistant applications.