The knowledge of steady-state temperature distribution is known a priori for natural convection stability analysis. The present study determines the temperature profiles in an infinite horizontal layer of fluid filled with saturated porous medium confined between two convective surfaces subjected to external radiative incidence and imposed downward convection. The investigation concentrates on the influences of the thermal boundary condition (Biot number), internal and external Rayleigh numbers, Peclet number optical thickness, and surface reflectivities. The implications of these factors on fluid stability are addressed in detail.