The temperature-dependent ideal shear strength (τ_IS) of γ′-Ni₃Al and the effects of alloying (Re, Ru, Mo, Cr, Co, W, and Ta) were studied in terms of first-principles calculations within the {111} slip plane along the [11−2] and [−110] directions. Based on the predicted volume versus temperature relations, the temperature dependence of τ_IS was obtained using the quasistatic approach, where it was found that τ_IS gradually decreased with increasing temperature. For the {111}[11−2] slip systems, all of the alloying elements except for Co were found to improve the τ_IS of γ′-Ni₃Al at the considered temperature. Among these elements, Re was the most effective element, and doping a small amount of Re (∼3 at%) was found to increase τ_IS by ∼23.5% at 0 K. Next, W and Mo increased the τ_IS by 20.2 and 18.1%, respectively. For the {111}[−110] slip systems, only Re increased the τ_IS of γ′-Ni₃Al while the other dopants decreased the ideal shear strength of the system at 0 K. Interestingly, a high-temperature relative strengthening via W alloying was observed for the γ′-Ni₃Al phase within the {111}[−110] slip system at temperatures T > 800 K. However, the sequence of the τ_IS of the γ′-Ni₃Al phase doped with other alloying elements was not altered by increasing temperature. According to these calculations, Re and W at the Al sites can effectively improve the shear resistance of the γ′-Ni₃Al phase, and especially at high temperature. Furthermore, the effect of alloying upon the shear strength is understood by the electronic structure analysis.