We present evidence for an isostructural, first-order Mott transition in MnO at 105±5 GPa, based on high-resolution x-ray emission spectroscopy and angle-resolved x-ray diffraction data. The pressure-induced structural and spectral changes provide a coherent picture of MnO phase transitions from paramagnetic B1 to antiferromagnetic distorted B1 at 30 GPa, to paramagnetic B8 at 90 GPa, and to diamagnetic B8 at 105±5 GPa. The last is the Mott transition, accompanied by a significant loss of magnetic moment, a ~6.6% volume collapse and the insulator-metal transition as demonstrated by recent resistance measurements.