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˗MnOx 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 MnOx 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-MnOx/PMS, MnOx/PMS, Co3O4/PMS, PMS, and adsorption were 100%, 27%, 33%, 17%, and 5%, respectively. The Co18-MnOx morphology, microstructure, textural properties, and catalytic efficiency were well-retained after recycling. Compared to SO4·− and ·OH, 1O2 and O2·− were the dominant ROS. The balance among redox couples of different species (Co2+/Co3+, Mn3+/Mn4+, O2−/O2) 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 MnOx for advanced oxidation processes and multipurpose applications.