Cation inversion in inverse spinel NiAl₂O₄ couples local coordination to macroscopic compressibility, yet its pressure evolution remains poorly constrained. Here, we quantify the inversion parameter i and oxygen positional parameter u by in situ X-ray diffraction in a diamond anvil cell. Rietveld refinements show that i increases from 0.753 at ambient pressure to 0.917 at 9.06 GPa, accompanied by a decrease of u over the same hydrostatic range. The unit-cell volume is well described by the equation of state fitted below similar to 10 GPa, yielding V ₀ = 514.7(7)& Aring;3, B ₀ = 238.53(15) GPa, and B ₀ ' = 5.31(14). The average tetrahedral A-O bond length decreases overall with pressure, whereas the octahedral B-O bond length changes only modestly. The normalized average tetrahedral polyhedral volume decreases systematically, while the normalized octahedral polyhedral volume remains close to its ambient-pressure value within uncertainty. These results indicate that pressure-driven densification in NiAl₂O₄ involves coupled evolution of lattice compression, oxygen-framework relaxation, and cation redistribution, with a stronger relative response of the tetrahedral coordination environment over the investigated hydrostatic range.