This study presents a facile strategy to construct three-dimensional graphene network (3DGN) and metal–organic framework (MOF)-derived metal oxide composites as free-standing electrodes for supercapacitors for the first time. A Mn-based MOF is first grown in situ on a 3DGN substrate through a simple solution immersion method, and then a high-temperature treatment has resulted in the formation of a 3DGN decorated with Mn₂O₃ with a nanowire stacking flower-like morphology. The structure and morphology of the as-prepared samples are investigated by powder X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy analysis, scanning electron microscopy, elemental mapping, and transmission electron microscopy. The designed 3DGN/Mn₂O₃ electrode material exhibits a high specific capacitance of 471.1 F g⁻¹ (0.21 F cm⁻²) at 0.2 A g⁻¹, good rate capability of 57.3% at 5 A g⁻¹ relative to the initial value at 0.2 A g⁻¹, and excellent long-cycle stability without decaying after 1800 charge–discharge cycles. The remarkable electrochemical performances originate from the synergistic effect of the high electrical conductivity and large surface area of the 3DGN along with the superior pseudocapacitance activity of Mn₂O₃ nanowires. This result suggests that the 3DGN/MOF-derived metal oxide composites are promising and efficient binder-free electrode materials for high-performance supercapacitors.