[en] Highlights: • MRCI potentials and transition moments are computed. • Lifetime of B state in excellent agreement with two of the three experiment. • Lifetime of the d state is in good agreement with experiment. • Lifetime of the D state is longer than experiment. The low-lying singlet and triplet states of MgO have been studied using a SA-CASCF/IC-MRCI approach using the aug-cc-pV5Z basis set. The spectroscopic constants ($r_e\text{,}{\omega }_e$, and $T_e$) are in good agreement with the available experimental data. The computed lifetime for the B state is in excellent agreement with two of the three experimental results. The d state lifetime is in good agreement with experiment, while the computed D state lifetime is about twice as long as experiment.