The rational design of an asymmetric supercapacitor (ASC) with an expanded operating voltage window has been recognized as a promising strategy to maximize the energy density of the device. Nevertheless, it remains challenging to have electrode materials that feature good electrical conductivity and high specific capacitance. Herein, a 3D layered Ti₃C₂T_X@NiO-reduced graphene oxide (RGO) heterostructured hydrogel was successfully synthesized by uniform deposition of NiO nanoflowers onto Ti₃C₂T_X nanosheets, and the heterostructure was assembled into a 3D porous hydrogel through a hydrothermal GO-gelation process at low temperatures. The resultant Ti₃C₂T_X@NiO-RGO heterostructured hydrogel exhibited an ultrahigh specific capacitance of 979 F g^-1 at 0.5 A g^-1, in comparison to that of Ti₃C₂T_X@NiO (623 F g^-1) and Ti₃C₂T_X (112 F g^-1). Separately, a defective RGO (DRGO) hydrogel was found to exhibit a drastic increase in specific capacitance, compared to untreated RGO (261 vs 178 F g^-1 at 0.5 A g^-1), owing to abundant mesopores. These two materials were then used as free-standing anode and cathode to construct an ASC, which displayed a large operating voltage (1.8 V), a high energy density (79.02 Wh kg^-1 at 450 W kg^-1 and 45.68 Wh kg^-1 at 9000 W kg^-1), and remarkable cycling stability (retention of 95.6% of the capacitance after 10,000 cycles at 10 A g^-1). This work highlights the unique potential of Ti₃C₂T_X-based heterostructured hydrogels as viable electrode materials for ASCs.