  We study the electronic structure, magnetic state, and phase stability of
paramagnetic BiNiO$_3$ 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 BiNiO$_3$ exhibits an anomalous
negative-charge-transfer insulating state, characterized by charge
disproportionation of the Bi $6s$ states, with Ni$^{2+}$ ions. Upon a
compression of the lattice volume by $\sim$4.8\%, BiNiO$_3$ is found to make a
Mott MIT, accompanied by the change of crystal structure from triclinic
$P\bar{1}$ 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
Ni$^{2+}$ across the MIT, which is incompatible with the valence-skipping
Ni$^{2+}$/Ni$^{3+}$ model. Our results suggest that the pressure-induced change
of the crystal structure drives the MIT in BiNiO$_3$.
