This article focuses on the onset of dissolution-driven convection in an inclined porous layer and explores the influence of several important control parameters, including the inclination angle, Damköhler number, and Rayleigh number. Our investigation reveals that the boundaries of linear instability and nonlinear stability do not align, indicating that different behaviors occur in these regions of parameter space. As the inclination angle increases, the subcritical instability region expands, indicating a wider range of conditions where subcritical instability can occur. Moreover, transverse rolls demonstrate greater stability when compared to longitudinal rolls, highlighting the significant impact of convection pattern orientation on stability. Furthermore, both the Damköhler number and inclination angle have stabilizing effects on the system, contributing to increased stability. Moreover, the subcritical region between longitudinal and transverse rolls appears to expand.