Hot Isostatic Pressing (HIP) is a manufacturing process that consolidates powders of metallic materials to produce near-net-shape components with theoretical density. In this process, the material powder is enclosed in a die which is then subjected to high temperature and pressure in a closed container filled with inert gas such as argon. In the initial stages of the process, when both the pressure and temperature are increased, the particles undergo plasticity driven deformation and neck formation leading to significant pore closure. Subsequently, temperature and pressure are held constant during which further pore closure is attained through diffusion mediated mechanisms. While this process has found widespread use to manufacture defect free high-end components such as turbine discs precise control of process parameters is necessary to avoid localized porosity and deviation from desired final geometry. Thus, various thermo-elasto-viscoplastic-densification continuum models have been developed to perform optimization of HIP process parameters. However, these models are chiefly phenomenological and are weakly connected to particle scale behavior through some material constants. In order to address this shortcoming, development of particle scale model of HIP is necessary. Though a wide range of phase-field-based models of sintering can be found in the literature, similar attempts to capture the behavior of particle aggregates during HIP is lacking. A key limitation being the initial large deformation and instantaneous plasticity in this process, as well as the exceedingly large computational cost associated with 3D phase-field simulations. In this work, a 3D thermo-mechanical Finite Element Method (FEM) micro-model of particle interaction has been developed to obtain accurate macroscale constitutive behavior during HIP. In the micro-model a body-centered cubic arrangement of particles has been considered assuming average size and initial packing factor of 0.68, which is close to the typical packing density after initial compaction. The particles in the Representative Volume Element (RVE) have been assumed to have an isotropic elastic plastic creep (both dislocation and diffusional) behavior. Since, the diffusivities are higher on the surfaces and at the particle contact regions, a thin layer of elements at the particle surfaces have been assigned larger diffusivities in the creep model. The RVE has been subjected to various macroscopic deformation gradients histories in addition to periodic boundary conditions to perform microscale FEM simulations. The macroscopic stress–strain and density evolution has been obtained using the temperature dependent properties for Inconel 718 and compared with a macroscopic model based on Abouf and Downey. The comparisons show that the microscale RVE analysis provides similar volume averaged responses as the macro-constitutive model, demonstrating the usability of the multi-scale approach to derive physics-based microstructure dependent constitutive models of HIP.