The present study investigates the effect of porous walls on the thermo-hydraulic characteristics of tapered Double Layer Microchannel Heat Sink (DL-MCHS). Three tapered DL-MCHS with different porous walls arrangements is simulated and compared for varying tapering of the channel and Reynolds number considering water and nanofluid as coolant. The fluid flow through porous media and micro-channel is modeled using the Darcy-Brinkman-Forchheimer equation and Navier-Stokes equation respectively. The above two equations coupled with continuity and energy equations are solved numerically to depict the thermo-hydraulic characteristics of DL-MCHS. It is demonstrated that the porous walls reduce the pressure losses along with a reduction in cooling performance of tapered DL-MCHS making the use of porous walls non-viable. However, incorporating porous walls in either bottom or top channel enhances the thermal performance and the overall performance making the use of porous walls viable. Also, the use of Al2O3-H2O nanofluid enhances the performance of a heat sink further by 11% as compared to water. It is found that incorporating porous walls only in the bottom channel gives the best performance among all three porous arrangements. Finally, through an optimization study, the enhancement in thermal performance by 22.7% is reported considering TF = 0.5, Re = 600, and nanofluid as coolant making it an optimum viable design.