In this work, we have investigated the structural, electronic and optical properties of zinc-blende (ZB) GaAs1−xBix ternary alloys at normal and under hydrostatic pressure. Firstly, we have performed the calculation of the structural and electronic properties of binary compounds GaAs and GaBi and for GaAs1−xBix ternary alloy at different compositions x=0.0625, 0.125, 0.25, 0.5 and 0.75. It is observed that lattice parameter increases with increasing Bi content; however the direct band gap EgΓ-Γ of GaAsBi decreases non-linearly. We have studied the variation of the spin–orbit splitting energy Δso with respect of Bi compositions. Our study shows that the Δso exceeds the energy gap Eg for bismuth fractions greater than 15%. We have also studied the effect of hydrostatic pressure on the structural, electronic and optical properties of the GaAs0.9375Bi0.0625, GaAs0.875Bi0.125 and GaAs0.75Bi0.25. We found that the application of hydrostatic pressure leads to variation of the electronic and optical properties of these materials.