The porosity parameter serves as a pivotal factor in determining the resistance exerted by a porous medium on fluid motion, especially in magnetohydrodynamic (MHD) flows. This study presents a novel numerical investigation of the coupled influence of porosity, viscous dissipation, and Joule heating on both momentum and thermal boundary layers over a porous surface. The results demonstrate that increasing porosity enhances medium permeability, thereby reducing hydrodynamic drag and intensifying the velocity gradient near the stagnation region. Conversely, lower porosity impedes fluid penetration, resulting in diminished velocity and a compressed boundary layer structure. While the direct impact of porosity on thermal transport is minimal, its interaction with dissipative effects leads to subtle modifications in temperature distribution. The graphical and quantitative findings underscore the importance of fine-tuning the porosity parameter to regulate flow resistance and thermal behaviour in advanced MHD systems. The methodology employed based on robust numerical simulations offers a comprehensive framework for analysing porous flow dynamics in engineering and energy applications, highlighting the novelty of integrating complex interdependencies between porosity and thermophysical mechanisms.