The present work reports fabrication of trilaminar core–shell composites of Fe3O4@C@PANI as efficient lightweight electromagnetic wave absorber by facile hydrothermal method and subsequent high-temperature calcination followed by its encapsulation through oxidative polymerization of aniline. The prepared composite structure was characterized by FTIR, XRD, XPS, TEM, HRTEM, and SQUID. The measurement of reflection loss, complex permittivity, complex permeability, and total shielding efficiency of the composites has been carried out in the frequency range of 2–8 GHz. Our findings showed lowest reflection loss (∼33 dB) in composite comprised of Fe3O4@C:aniline (1:9 wt/wt) corresponding to shielding efficiency predominantly due to absorption (∼47 dB) than reflection (∼15 dB). Such high value of shielding efficiency could be ascribed to the presence of dual interfaces and dielectric–magnetic integration in Fe3O4@C@PANI. In all probability, higher dielectric loss through interface polarization and relaxation effects in Fe3O4@C@PANI could also contribute toward superior microwave absorption ability of Fe3O4@C@PANI compared to Fe3O4@C and Fe3O4/PANI binary composites. This is likely to enhance the interfacial polarization, natural resonance, dielectric polarization, trapping of EM waves by internal reflection, and effective anisotropy energy in Fe3O4@C@PANI.