The current research work is focused on the development of a combined micromechanical model of transformation and twinning induced plasticity mechanisms in austenite based high Mn steels. Both mechanisms are combined by incorporating transformation in twinning based crystal plasticity model. Initially, mechanical twinning is incorporated in slip based crystal plasticity model. Afterwards, transformation phenomenon (austenite to martensite) is included in the developed slip and twin based crystal plasticity model. The kinematics of the mechanisms is developed by defining elastic, plastic, and transformation deformation gradients. These deformation gradients are then used to calculate stress tensors. The constitutive equations in terms of integration algorithm are implemented in ABAQUS as a user-defined subroutine. Three dimensional finite element model of single and polycrystal austenite are developed. Single austenite crystal is represented by one finite element while the behavior of polycrystal austenite is estimated through 500 grains. The orientation of each grain is defined through Euler angles. The performance of the model is evaluated through finite element simulations in order to predict the elastic-plastic and transformation behaviors of single and polycrystal austenite under different loading conditions i.e. uniaxial tension and simple shear. The developed model is in good agreement with published literature. In simple shear, prominent difference in stress magnitude is found once twinning mode is incorporated in slip and transformation. This difference has significant magnitude in case of polycrystal austenite. This shows substantial advantage (in terms of strength and formability) of incorporating mechanical twinning along with slip and transformation.