Direct pyrolysis of SnO2 nanoparticles mixed with bisphenol-BA/aniline polybenzoxazine yields highly graphitized, Sn metal doped porous carbon material (Sn–C). The prepared Sn–C was used as a reinforcement for the development of composites with bisphenol-BA and furfuryl amine based polybenzoxazine (poly(BBA-ffa)). The maximum degradation temperature of the Sn–C reinforced poly(BBA-ffa) composites reached to 526 °C with 65% char yield. The value of electrical conductivity of the prepared composites increased from 2.79 × 10−8 S/m to 7.51 × 10−2 S/m. Further, it was also observed that the developed composites possess the high dielectric behavior with increased value of dielectric constant from 3.47 to 10.05. The enhancement of electrical conductivity leads to the effective electromagnetic interference shielding of the polybenzoxazine composites. The highest weight percentage loading of Sn–C shows the EMI SE value of 33.23 dB with shielding effectiveness of 99.95%. The developed polybenzoxazine composites can be utilized for high temperature resistant EMI shielding material.