Recently, bimetallic selenides have been considered as efficient electrocatalysts towards various electrochemical applications. Here, we demonstrated the synthesis of different transition metals (M = V, Zn, Mn, and Cu) incorporated into CoSe₂ (M–CoSe₂). The pseudocapacitive behaviours of the M–CoSe₂ were enhanced due to the introduction of multiple redox properties and greater intrinsic electronic conductivity. Among them, bimetallic V–CoSe₂ deposited on nickel foam (V–CoSe₂/NF) exhibited a substantial specific surface area, high specific capacitance (1830.2 F g⁻¹ at 1.5 A g⁻¹), long-term cycling stability (118% retention, 5000 cycles) and low internal charge transfer resistance (R_ct = 36.74 Ω). Thus, an asymmetric device assembled from V–CoSe₂ and activated carbon (AC) exhibited an excellent energy density of 103.03 W h kg⁻¹ at a power density of 1200 W kg⁻¹. In summary, this work presents a new strategy to develop defect-rich transition metal selenides for high energy density supercapacitor devices.