The present work describes the development of sustainable bio‐benzoxazines for oil water separation and its composites for applications where a low dielectric constant is required. In addition, cardanol benzoxazine monomers (C‐ida and C‐pyta) with low curing temperature were designed with inbuilt catalytic core using two different heterocyclic amines, namely tetra aryl imidazole diamine (ida) and pyridine core triamine (pyta). Cotton fabric coated with poly(C‐ida) and poly(C‐pyta) show water contact angle values of 160° and 164°, respectively. The oil‐water separation efficiency of the polybenzoxazines coated cotton fabrics was 95%. Further, the poly(C‐ida) and poly(C‐pyta) matrices were reinforced with varying weight percentages (1, 3, 5, 7, and 10 wt%) of glycidylpropoxytrimethylsilane‐functionalized biosilica. The benzoxazine matrices and composites obtained were characterized using different analytical techniques in order to assess their molecular structure, cure behavior, thermal stability, morphology, surface, and dielectric behavior. Data obtained from different studies suggest that these matrices and composites can be used as coatings for oil‐water separation and high‐performance micro‐electronics insulation applications under adverse environmental conditions.