MXene-based materials are promising electrode materials for supercapacitors. Herein, Ni2CO3(OH)2 nanosheets and/or nanoparticles are in-situ grown on the surface of two-dimensional (2D) Ti3C2 to form Ti3C2/Ni2CO3(OH)2 composites during one-pot hydrothermal processing. The uniform distribution of Ni2CO3(OH)2 on Ti3C2 is due to the electrostatic interaction between positively charged nickel ions and negatively charged Ti3C2. Importantly, the electrochemical performance of Ti3C2/Ni2CO3(OH)2 are enhanced. The 30-Ti3C2/Ni2CO3(OH)2 composite electrode exhibits a specific capacity of 173.8 mAh g−1 at 1 A g−1 and excellent cycling stability (capacity retention of 80.1% after 5000 cycles at 10 A g−1). The hybrid supercapacitor using 30-Ti3C2/Ni2CO3(OH)2 composite as positive electrode and active carbon as negative electrode delivers a high energy density of 28.2 Wh kg−1 at a power density of 374.8 W kg−1. The super performance of the composite electrode is attributed to the synergistic effects of good redox activity of Ni2CO3(OH)2 particles combined with high electronic conductivity of 2D Ti3C2. The excellent electrochemical performance of Ti3C2/Ni2CO3(OH)2 composite indicates its potential as a promising electrode material to high energy/power density energy storage devices.