The stilling basins are used for dissipating the flow energy in spillways. The hydraulic performance of the stilling basin is dependent on the shape and dimension of the basin. The literature review indicates that the convergence of the side walls of the stilling basin enhances the efficiency of the stilling basin and stabilizes the jump within the basin. The research aimed to investigate the hydraulic performance of USBR type III stilling basin by modifying its standard geometry. The stilling basin of the Mohmand Dam spillway located on the Swat River; Pakistan was selected as a study area. The model was operated with parallel walls of stilling basin and by converging the walls of stilling basin from 1° to 5°. The results indicated that the efficiency of the hydraulic jump with converged wall stilling basin has improved as compared to parallel walls and loss of energy increased due to convergence. The efficiency of stilling basin increased up to 4% with the increment in wall convergence, but the optimum efficiency of the hydraulic jump was obtained at 3° wall convergence. The results also indicated that an increase in convergence angle leads to an increase in bottom pressures. Furthermore, the modified baffle blocks increased the energy dissipation efficiency to 1% as compared to standard baffle blocks. The study concludes that wall convergence not only improves the hydraulic performance of the stilling basin but also reduces the construction cost of the stilling basin.