This study reports for the first time the lattice parameters and the complete crystal structure evolution with increasing pressure for a thiospinel with composition CuCr1.7V0.3S4 (space group Fd3̄m) measured by single-crystal X-ray diffraction as a function of pressure up to 7 GPa. The P-V data are adequately described to a fourth-order Birch-Murnaghan equation of state with the following coefficients: V0 = 947.86(6) Å3, KT0 = 88(1), and K′ = 6.3(9), K″ = −1.1(4). This is the first time that the compressibility behavior of a spinel structure has been described by a fourth-order Birch-Murnaghan equation of state. The unit-cell volume shows a compression of about 6.3% over the entire pressure range investigated. The crystal structure evolution clearly indicates that the main compression mechanism is related to the compression of the CuS4 tetrahedron, which is significantly greater than the CrS6 octahedron. The tetrahedral volume decreases by 7.8% over the pressure range studied while the octahedral volume decreases by 5.5%. The change in the octahedral volume is accompanied by a decrease in the angular distortion of the CrS6 octahedra.