The material, SA333 Grade-6 C-Mn steel, is tested for balanced 90° out-of-phase (non-proportional) tension-torsion (biaxial) cyclic loading. Experimental results show predominant cyclic softening with, cross hardening and non-proportional hardening due to the non-parallel strain-path changes. Strainpath changes lead to activation of new slip systems. Dislocation interactions between the ‘already active’ slip systems and ‘just active’ or ‘still non-active’ slip systems may develop latent hardening effect. Present work deals with the modelling of non-proportional hardenings based on latent hardening mechanism for the material. Kinematic hardening rule is used to capture the effects of the interactions of mobile dislocation in planar slip systems. The cyclic softening behaviour of the material is modelled by the annihilations of dislocations forming low angle sub-grain boundary. The material model is plugged into ABAQUS as user material subroutine to simulate non-proportional hardening, cross hardening and other cyclic plastic behaviour for the material. The simulated results are compared with the experimental results and convincing agreements are observed.