In the present investigation, pitch derived mesocarbon spheres (MCS) with nickel nanoparticles based nanocomposites have been developed and first time reported as an excellent electromagnetic interference (EMI) shielding material in X-band (8.2–12.4 GHz) frequency region. A simple and economical method has been used for the synthesis of MCS from heat treatment of coal tar pitch and petroleum pitch. As synthesized MCS powder was semi-graphitized at 1400 °C, it is called graphitized mesocarbon spheres (GMCS) followed by chemical treatment to form expanded mesocarbon spheres (EMCS). Ni nanoparticles were synthesized in-situ using above three materials (MCS, GMCS and EMCS) to form MCS-Ni, GMCS-Ni and EMCS-Ni composite. The investigation revealed that EMCS-Ni composite exhibit excellent absorption dominated EMI shielding effectiveness (SEA) of −72.3 dB (∼400% increment in absorption) with a total SE (SET) of −81.5 dB at 8.2 GHz which is remarkably high as compared to other reported values in literature.