Hierarchical micro-/nano-structures assembled by two-dimensional (2D) nanomaterials are promising electrode materials for energy storage devices, owing to their unique structures and synergetic effects. Metal–organic frameworks (MOFs) are versatile templates for various hierarchically structured nanomaterials with high-performance in energy storage applications. However, it is still a great challenge to achieve precise control of the structure and composition of MOF-derived nanomaterials, especially for those composites with two or more components. In this work, a facile strategy for the preparation of MOF-derived 2D assembled Ni–Mn–C ternary composites, which are composed of Ni(OH)₂ and MnO₂ nanosheets decorated on a carbon matrix (Ni(OH)₂–MnO₂/C), is developed. Due to its high surface area, good electrical conductivity and the synergistic effect among components, the Ni(OH)₂–MnO₂/C composite exhibits excellent electrochemical performance, especially high-rate performance (574.0 F g⁻¹ at 40 A g⁻¹) and cycling stability (capacitance retention of ∼87% at 2 A g⁻¹ over 10 000 cycles). In addition, the Ni(OH)₂–MnO₂/C composite-based all-solid-state supercapacitor delivers high power density, good cycling stability and excellent flexibility.