An economical and environment-friendly material as a catalyst is highly desirable to activate peroxymonosulfate (PMS) into reactive oxygen species (ROS). Cobalt-doped dumbbell-shaped manganese oxide (CoX˗MnO where X = 1.0, 6.0, 12.0, 18.0, and 24.0 mM) was synthesized as a PMS-activator for degrading organic pollutants in wastewater. We have developed a green, facile, and low-temperature route without any organic solvents, and templates to synthesize Co-doped dumbbell-shaped MnO with hierarchical porosity. It is the first-ever research to use these materials for peroxymonosulfate activation. The microstructure contained nanoparticles that self-assembled into a maze-like dumbbell-shaped mesostructure. Phenol degradations after 9 min of Co18-MnO/PMS, MnO/PMS, CoO/PMS, PMS, and adsorption were 100%, 27%, 33%, 17%, and 5%, respectively. The Co18-MnO morphology, microstructure, textural properties, and catalytic efficiency were well-retained after recycling. Compared to SO and OH, O and O were the dominant ROS. The balance among redox couples of different species (Co/Co, Mn/Mn, O/O) and PMS decomposition enabled ROS production. The high catalytic activity was assigned to the Mn/Co synergism, hierarchical microstructure, and ROS. Furthermore, the DFT study investigated the difference between the activation mechanism of PMS (adsorption and electron transfer) on MnOx and Co-MnOx surfaces. Our research devised a facile procedure to synthesize other transition metals doped MnO for advanced oxidation processes and multipurpose applications.