A fully coupled three-dimensional (3D) thermo-hydro-mechanical (THM) model is developed for simulating the complex multiphysics process of permafrost thaw. The 3D formulation allows the analysis of thaw consolidation problems with complex geometry and boundary conditions. The thermal, hydraulic, and mechanical fields are coupled in this model. Governing equations are derived based on the laws of conservation of each field: conservation of energy for the thermal field, conservation of mass for the hydraulic field, and conservation of momentum for the mechanical field. Physical processes such as heat conduction, phase change, thermal convection, fluid flow due to pore water pressure, elevation, thermal gradients, and force equilibrium based on effective stress theory are considered in this model. The model is then applied to simulate the thaw consolidation of permafrost. The simulation results show that excess pore water pressure is generated in the soil during thawing. The soil then experiences a time-dependent settlement following the dissipation of excess pore water pressure. The results prove that the THM model adequately captures the thaw consolidation process of permafrost.