Reduced graphene oxide (RGO) has been widely applied in the field of electromagnetic wave (EMW) absorption. However, its excessively high conductivity results in poor impedance matching, causing the incident waves to undergo intense reflection and weak absorption. In this work, nitrogen-doped reduced graphene oxide/magnesium ferrite@nitrogen-doped carbon (NRGO/MgFe₂O₄@NC) composite aerogels were prepared by solvothermal synthesis, in-situ polymerization, annealing treatment, and hydrothermal self-assembly processes. Significantly, the ternary composite aerogels exhibited the ultralow bulk density and a unique three-dimensional (3D) porous network structure. Furthermore, the MgFe₂O₄ microspheres were uniformly coated with the NC layer, and a special chain-like core–shell structure was observed, which could form abundant heterogeneous interfaces. It was notable that when the addition amount of MgFe₂O₄@NC was 30 mg and the filling ratio was 6 wt.%, the minimum reflection loss was −59.79 dB at a matching thickness of 3.3 mm, and the maximum effective absorption bandwidth reached 7.2 GHz at a thickness of 2.83 mm. The synergistic effect of multiple reflections, conduction loss, polarization loss, and eddy current loss, as well as the optimized impedance matching, significantly enhanced the EMW absorption performance. The research results of radar cross section (RCS) simulation demonstrated that the NRGO/MgFe₂O₄@NC composite aerogel had excellent radar stealth performance. Additionally, the prepared ternary composite aerogels exhibited good thermal insulation property. Therefore, the prepared ternary composite aerogels could be used as lightweight and multifunctional EMW absorbers.