In this paper we present the results of ab initio model potential embedded cluster average coupled pair functional calculations on (VCl6)3− embedded in a reliable representation of the Cs2NaYCl6 host. They are aimed at complementing recent high pressure, room temperature, broad band luminescence studies with detailed theoretical data. In particular, we study the effects of high hidrostatic pressure (i) on the structure of V3+ substitutional defects in four low lying electronic states (a3T1g, 3T2g, 1T2g, and b3T1g), (ii) on the individual a1g and eg force constants and equilibrium displacements, and (iii) on the zero-phonon and Franck–Condon energy differences between them. It is shown that only the eg equilibrum displacements between different electronic sates are large and pressure dependent, while the a1g ones are small and essentially pressure independent. A value of κ = 4×10−3 kbar−1 is suggested for the isothermal bulk modulus of the Cs2NaYCl6 elpasolite, because it allows for an excellent match between the theoretical dependence on the unit cell volume and the experimental dependence on applied pressure of several properties: equilibrium displacements, vibrational frequencies, and minimum-to-minimun and vertical energy differences.