With the rapid development of telecommunications and microwave technologies and the introduction of these technologies into human life, the need to obtain advanced materials to reduce the effects of these waves in specific and sensitive areas has been highly considered. Here, we have investigated the structural, morphological, magnetic, and electromagnetic interference (EMI) shielding properties of N-doped reduced graphene oxide (NRGO) decorated with La-doped Zn-Cu-Ni ferrite nanocomposite using XRD, FESEM, TEM, HRTEM, VSM, and vector network analyzer (VNA) tests. The hydrothermal method was used to prepare nanocomposites, and the graphene’s atomic structure remained intact during the synthesis process. The nanocomposites are soft magnetic materials, and NRGO can be employed to optimize the magnetic properties. Some types of nanocomposites are approved to have unique EMI shielding properties, where the shielding effectiveness is above 20dB on almost the entire range of 2–18 GHz with a thickness of just 2 mm. The scientific origin of all changes in electrical and magnetic properties has been comprehensively investigated. Most of the shielding effectiveness comes from absorption. Therefore, the nanocomposites are lightweight and excellent absorption-dominant EMI shielding materials that can reduce the energy of electromagnetic waves by 99% over the wide range of 2–18 GHz.