Sewage sludge-derived mesoporous biochars (SS-MBCs) were prepared by using cationic polyacrylamide (PAM(+)) as a template agent through a template-like method under high temperature and employed for getting rid of methylene blue (MB) from water. Textural evolution, mesostructured morphology, thermodynamic properties, and surface chemical groups of SS-MBCs were analyzed. It showed that PAM(+) not only played an important role in good nucleation that brought well-developed texture and novel pore size distribution to SS-MBCs but also improved the MB adsorption capacities of SS-MBCs by increasing the specific surface area and the content of oxygen functional groups, especially the lactone. Preparation factor analysis indicated that PAM(+) concentration, dosage of additive sludge, and carbonization temperature had distinct effects on material structure and adsorption performance especially above the pyrolytic temperature of 800 degrees C. The adsorption kinetics and isotherms were analyzed in detail, and it revealed that the kinetics and equilibrium adsorptions of SS-MBCs could be well-described by the Langmuir isotherm model and pseudo-second-order kinetics, respectively. Remarkably, the SS-MBCs showed higher removal efficiency and adsorption capacity than commercial activated carbon and most reported sludge-based adsorbents.