Abstract: The preparation of carbon-based electromagnetic wave (EMW) absorbers possessing thin matching thickness, wide absorption bandwidth, strong absorption intensity, and low filling ratio remains a huge challenge. Metal–organic frameworks (MOFs) are ideal self-sacrificing templates for the construction of carbon-based EMW absorbers. In this work, bimetallic FeMn–MOF-derived MnFe₂O₄/C/graphene composites were fabricated via a two-step route of solvothermal reaction and the following pyrolysis treatment. The results reveal the evolution of the microscopic morphology of carbon skeletons from loofah-like to octahedral and then to polyhedron and pomegranate after the adjustment of the Fe³⁺ to Mn²⁺ molar ratio. Furthermore, at the Fe³⁺ to Mn²⁺ molar ratio of 2:1, the obtained MnFe₂O₄/C/graphene composite exhibited the highest EMW absorption capacity. Specifically, a minimum reflection loss of −72.7 dB and a maximum effective absorption bandwidth of 5.1 GHz were achieved at a low filling ratio of 10wt%. In addition, the possible EMW absorption mechanism of MnFe₂O₄/C/graphene composites was proposed. Therefore, the results of this work will contribute to the construction of broadband and efficient carbon-based EMW absorbers derived from MOFs.