A comprehensive study of benzoxazines derived from magnolol and five different substituted aniline moieties through Mannich condensation was carried out. The structural confirmation was ascertained using different spectral analyses. Mg-a exhibited a lowest polymerization temperature of 220 °C than that of other monomers. Whereas, poly (Mg-ea) showed relatively the higher initial thermal stability until 411 °C with char yield of 56 % at 850 °C and enhanced values of limiting oxygen index (LOI) and statistic heat resistance index (HRI) than rest of polybenzoxazines. The Mg-pfa benzoxazine monomer exhibits significant antibacterial behavior with a maximum of 22 mm zone of inhibition and less cytotoxicity with IC50 value of 162 μg/ml as well as better corrosion resistant properties with 99 % corrosion inhibition efficiency. The hydrophobic studies indicated that poly (Mg-tfa) exhibited the highest water contact angle (CA) value of 143°. Poly (Mg-tfa) coated cotton fabric was resistant to chemical and UV treatments along with the 97 % of oil water separating efficiency. Polybenzoxazine composites were derived from poly (Mg-fa) matrix and cashew nut shell residue ash (CNA) and cashew nut shell carbon (CNC) fillers to ascertain influence on thermal, dielectric and hydrophobic properties. Poly (Mg-fa) composites reinforced with 15 wt% of CNA and 15 wt% of CNC exhibited dielectric constant values of 2.71 and 6.91 respectively at a frequency of 1 MHz. Findings from multifaceted studies indicate that the polybenzoxazines and composites reported in the present work can be utilized for anti-corrosion, anti-microbial, oil-water separation and electronic applications for improved performance and enhanced longevity.