The electronic structure, optical and thermoelectric properties of half-Heusler ZrIrX (X $$=$$ = As, Sb, Bi) compounds were investigated under pressure by using the modified Becke and Johnson exchange potential. The band gaps of ZrIrAs and ZrIrBi increase from tensile strain ( $$\varepsilon $$ ε $$=$$ = 5%) to compressive strain ( $$\varepsilon $$ ε $$=$$ = $$-5$$ - 5 %), and at about $$\varepsilon $$ ε $$=$$ = $$-4$$ - 4 % they changed from indirect to direct band gaps. Their absorption efficiencies increase from compressive to tensile strain in the low energy ( $$ \leqslant $$ ⩽ 2.8 eV). For p-type doped compounds, the Seebeck coefficients and the power factors increase from tensile to compressive strain. While the the Seebeck coefficients and the power factors of n-type compounds, first increase and then decrease from tensile to compressive strain, reaching the largest values at the critical strain (direct-indirect transition). ZrIrSb is an indirect band gap insulator, but it translates to direct band gap insulator when the tensile strain $$\varepsilon \geqslant $$ ε ⩾ 2%.