A phenomenological constitutive relation, for capturing the shear band formation in a rate-independent elastic-plastic material, is established. The model takes into account both the J2-isotropic flow and a threshold shear stress-based flow. The elastic-plastic constitutive tensor is expressed explicity in terms of elastic constants, the deviatoric stress tensor, the direction of the principal shear velocity-strain, and other material constants. This model particularly facilitates the resolution of the formation of the shear band even under material hardening conditions and does not demand an a priori knowledge of the orientation of the shear band. This is incorporated in an FEM, and the plane strain tensile test of Anand and Spitzig  is numerically simulated. The computed results compare favorably with the experimental data. The shear band emerges more naturally as a solution to the boundary value problem, unlike the situations in solutions based on classical bifurcation methods. Nevertheless, the usefulness of the local instability condition (Ortiz et al. ) is also demonstrated.