<p>Herein, we present the first principles study of the structural, electronic, elastic, optical, magnetic, and thermodynamic properties of the double perovskite Sr₂NiMoO₆ under hydrostatic pressure (0–20 GPa). Structural optimization and total-energy analysis confirm the ferromagnetic configuration as the ground state, with pressure inducing systematic lattice compression and enhanced mechanical stability. Elastic coefficients and moduli grow monotonically with pressure, suggesting substantial stiffening without loss of ductile behavior and low elastic anisotropy. Optical properties reveal pronounced pressure-induced modulation of the dielectric response, absorption, reflectivity, and refractive index, characterized by a consistent blue shift of optical features due to band structure reorganization. The magnetic moments are stable and almost pressure-independent, which affirms the stability of ferromagnetic ordering. Elastothermal and thermodynamic analyses show increasing sound velocities, Debye temperature, and melting temperature, accompanied by reduced thermal expansion and pressure-suppressed heat capacity at low temperatures. Overall, the hydrostatic pressure improves the structural rigidity, thermal stability, and optoelectronic tunability of Sr₂NiMoO₆, demonstrating its ability to be utilized in high-pressure and high-temperature environments.</p>