Ab initio based multireference singles and doubles configuration interaction calculations, which include relativistic effective core potentials of the constituting atoms, have been carried out to study the low-lying electronic states of GaBi. Potential energy curves and spectroscopic constants of the electronic states within 46 000 cm(-1) of energy have been reported. The ground-state dissociation energy of GaBi is calculated to be 1.24 eV as compared with the observed value of 1.60 +/- 0.17 eV. Effects of the spin-orbit coupling on the spectroscopic properties of some low-lying states below 25 000 cm(-1) have been studied. A large spin-orbit coupling produces a strong mixing among different A-S states and changes the characteristics of the potential energy curves. Several avoided crossings in the potential curves of 9 states of GaBi are also noted. The zero-field splitting of the ground state of GaBi is estimated to be 463 cm(-1). The A(3)Pi-X(3)Sigma(-) transition has been predicted to be quite strong. Three other transitions, namely, A(3)Pi-(3)Pi, 2(1)Sigma(+)-(1)Pi, and 2(1)Sigma(+)-(1)Sigma(+) are also studied. A few transitions from the A(3)Pi(0)(+) component, which survives the predissociation, are reported to be highly probable. The radiative lifetime of A(3)Pi(0)(+) is estimated, and the component is found to be shortlived. The oscillator strengths of 0(+)-0(+) and 0(+)-1 transitions for the lowest few vibrational levels are reported. A comparison of the electronic spectrum of GaX(X = P, As, Sb, Bi) molecules has been made.