Both Forced and mixed convection heat transfer effect of Al₂O₃/water nanofluid on the conjugate thermal performance of two-dimensional stepped lid-driven cavity under turbulent flow conditions are numerically investigated in the present study. A validated homogeneous heat transfer model within ANSYS FLUENT is used in the present study. Three cavity types namely: no step, forward step and backward step are used in the present study in relative comparison for Reynolds number, Re = 5000 to 9000 and Grashof number, Gr = 5000, 13000 and 20000. Al₂O₃/water nanofluid is considered with 1 vol.%, 2 vol.% and 3 vol.% nanoparticle concentrations. The effect of cavity type, convection type, Reynolds number, Grashof number, nanoparticle volume concentration on the thermal performance is evaluated in terms of average Nusselt number (Nu_avg) obtained at the fluid-solid interface. Nu_avg values obtained in the present study are higher for higher values of Gr and lowest interface temperature was recorded for backward step lid-driven cavity when compared with other cavity types that result in slightly higher performance. Moreover, at Re = 9000, 3 vol.% Al₂O₃ nanofluid exhibits 19.68% higher thermal performance in comparison with that of pure water. Furthermore, 467.79% higher thermal performance is observed in the case of 3 vol.% Al₂O₃ nanofluid at Re = 9000 when compared with the same working fluid at Re = 500 as available in the literature.