Summary Replacing oxygen in an oxide‐based material with sulfur can produce improved flexibility and more efficient electron transport in its structure leading to enhanced electrical performance. Herein, facile template‐free growth of free‐standing cobalt (II, III) oxide (Co3O4) on Ni foam via a mild hydrothermal technique followed by its transformation to cobalt (II, III) sulfide (Co3S4) via an ion‐exchange is reported. The microstructural morphology, phase, and porosity of the prepared Co3O4 and Co3S4 are characterized by FESEM, XRD, Raman, XPS, TEM, and BET analyses. The electrochemical performance of the Co3S4 film with a microporous morphology is considerably superior to that of Co3O4, exhibiting a high specific capacitance of 1604 F g−1 (905 F g−1 for Co3O4), the excellent restorative ability of ~99% at 1 A g−1 (~96% for Co3O4), and good retention of 98% at 10 A g−1 (~70% for Co3O4). The Co3S4 electrode shows excellent capacitance endurance even after 10 000 charge/discharge cycles and a high energy density of 128.32 Wh kg−1 at 0.72 kW kg−1. A fabricated symmetric Co3S4 supercapacitor device also reveals superior charge/discharge, restorative, and retention performances compared to a Co3O4 one. The excellent supercapacitive performance of phase‐transformed Co3S4 electrode is due its large electrochemically active surface area along with synergetic effect of small charge transfer resistance and high relative diffusion coefficient. Ion‐exchange synthesis of polyhedral Co3S4 on the three‐dimensional architecture of Ni foam with a desirable microporous morphology is reported along with its impressive electrochemical energy storage performance in alkaline KOH medium. The fabricated symmetric supercapacitor cell exhibits an outstanding supercapacitive performance due to the enhanced conductivity (resistivity ~10−4 Ω), low electronegativity, and efficient electron transport endowed with flexible material structure of Co3S4 than its oxide counterpart.