A spinel compound FeAl2S4 was successfully synthesized under high-pressure and high-temperature conditions and was systematically characterized via the structural, magnetic, and specific heat measurements. It crystallizes into a cubic structure with the space group Fd3̅m (no. 227) and the lattice constant a = 10.0207(2) Å. A Fe/Al site inversion is found; that is, the molecular formula can be rewritten as (Fe1-xAlx)(Al2-xFex)S4, and the inversion parameter x is about 0.22. Magnetic susceptibility measurements indicate that FeAl2S4 undergoes a spin glass behavior, which is confirmed by ac susceptibility and specific heat measurements. The freezing temperature Tf ∼ 10.5 K and Weiss temperature Tθ ∼ -107.4 K lead to a high frustration parameter f = |Tθ/Tf| of about 10, which suggests that FeAl2S4 is a high-frustration magnet. Our results indicate that high pressure can help stabilize the spinel structure with small R̅σ and the cation inversion plays an important role in the formation of the spin glass state.