First-principles results under high pressure have been obtained to give structural, elastic, electronic, vibrational, and thermodynamic properties of AsTh, which crystallizes in NaCl (B1) structure at 0 K and 0 GPa and turns into CsCl (B2) phase at approximately 17.7 GPa. Mechanical properties such as elastic constants, Young and isotropic shear modulus, Pugh and Poisson's ratios, Zener anisotropy factor, sound velocity, and Debye and melting temperatures have been obtained under pressure. Also, the electronic band structures and total-partial densities of states for both NaCl and CsCl structure have been investigated, and are in good agreement with the available theoretical results. AsTh in NaCl (B1) structure behaves in a brittle manner due to its Pugh and Poisson's ratios. Finally, phonon dispersion frequencies and phonon partial density of states have been obtained for both phases and they have been found to be dynamically stable.