We study the electronic structure, magnetic state, and phase stability of paramagnetic BiNiO3 near a pressure-induced Mott insulator-to-metal transition (MIT) by employing a combination of density functional and dynamical mean-field theory. We obtain that BiNiO3 exhibits an anomalous negative-charge-transfer insulating state, characterized by charge disproportionation of the Bi 6s states, with Ni2+ ions. Upon a compression of the lattice volume by ∼4.8%, BiNiO3 is found to make a Mott MIT, accompanied by the change of crystal structure from triclinic P1 to orthorhombic Pbnm. The pressure-induced MIT is associated with the melting of charge disproportionation of the Bi ions, caused by a charge transfer between the Bi 6s and O 2p states. The Ni sites remain to be Ni2+ across the MIT, which is incompatible with the valence-skipping Ni2+/Ni3+ model. Our results suggest that the pressure-induced change of the crystal structure drives the MIT in BiNiO3.