Two-dimensional (2D) MXenes (transition metal carbide or carbonitride) and metal–organic frameworks (MOFs) have emerged as appealing electrode materials for supercapacitors due to the advantages of each material and a 2D structure. However, a solitary MXene or MOF suffers from either inadequate redox reactive sites or low electronic conductivity and instability. Here, NiCo-MOF/MXene heterostructures are fabricated by assembling ultrathin 2D bimetallic NiCo-MOF nanosheets on exfoliated MXene nanosheets by a simple room-temperature ultrasonic method. The 2D/2D NiCo-MOF/MXene heterostructures combine the advantages of a MOF, MXene and hierarchical structure, i.e. a large surface area, a highly electrically conductive network, rapid ion diffusion and structural stability. As a result, the optimal NiCo-MOF/M₁₀ electrode exhibits a highly improved capacitance (1176.8 F g⁻¹vs. 653.4 F g⁻¹) and cycle life (72.5% vs. 50.5%), compared with the pristine NiCo-MOF. Moreover, a two-electrode cell using NiCo-MOF/M₁₀ as the cathode shows outstanding energy storage capability. This study provides an opportunity to enhance energy storage by designing 2D heterostructures.