For high-performance microwave absorption materials, component integration, structure tailorability and light weight are of practical significance. Herein, a new three-dimensional magnetic composite, namely carbon nanotubes (CNTs)-intercalated nitrogen-doped graphene (N-GN) embedded with Fe₂O₃ NPs (referred to as Fe₂O₃/N-GN/CNTs), were fabricated by a solvothermal method for use as synergistic microwave absorbers. Electronic microscopy investigation shows that the Fe₂O₃ NPs, which formed in situ, are uniformly dispersed on the N-doped graphene nano-sheets without aggregation and that the CNTs have been successfully inserted into the layers of nano-sheets. In addition, X-ray diffraction patterns (XRD), Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectrometry and a vector network analyzer (VNA) were used to investigate the structure, chemical composition, and electromagnetic parameters of the resulting Fe₂O₃/N-GN/CNTs composite. Taking advantage of the synergistic effect between Fe₂O₃ nanocrystals with magnetic loss and N-GN/CNTs with dielectric loss, the 3D Fe₂O₃/N-GN/CNTs composite shows excellent microwave absorption capabilities with highly efficient performance. A maximum reflection loss of −45.8 dB can be achieved at 9.32 GHz with a matching thickness of only 3 mm, and the effective absorption (below −10 dB) bandwidth reaches 14.5 GHz (3.5 to 18.0 GHz). The excellent microwave absorption of the as-prepared composites can be related to the integrated characteristics of good impedance matching and Debye relaxation, high attenuation, strong dipole polarization and interface polarization. Therefore, these results indicate that the newly designed Fe₂O₃/N-GN/CNTs composite is an ideal candidate for use as a synergistic microwave absorber to address electromagnetic pollution.