We have performed density functional calculations on the group II–IV nitride MgSiN2. At a pressure of about 20 GPa the ground state wurtzite derived MgSiN2 structure (LP-MgSiN2) transforms into a rock-salt derived structure (HP-MgSiN2) in agreement with previous theoretical and experimental studies. Both phases are wide band gap semiconductors with indirect band gaps at equilibrium of 5.58 eV (LP-MgSiN2) and 5.87 eV (HP-MgSiN2), respectively. As the pressure increases, the band gaps become larger for both phases, however, the band gap in LP-MgSiN2 increases faster than the gap in HP-MgSiN2 and with a high enough pressure the band gap in LP-MgSiN2 becomes larger than the band gap in HP-MgSiN2.