In the present work, we employed the DFT (Density Functional Theory) to investigate the electronic and magnetic properties of Ni₂MnGa Heusler alloy. We focused on the structural transition between tetragonal and cubic structures related to the band Jahn Teller effect. The structural electronic and magnetic properties are calculated for cubic and tetragonally distorted structures. According to the optimisation of total energy versus volume, the tetragonal phase is the ground state for Ni₂MnGa alloy 0 K. The band structure and density of state calculations show the ferromagnetic (FM) behaviour, with a total magnetic moment of 4.053 µ_B and 19.21% of spin polarisation at the Fermi level. Ni₂MnGa is a cubic compound above 276 K under a thermal effect, where it gets its shape memory behaviour. Applying uniaxial stress according to the z axis, the studied alloy undergoes a phase transition to the parent phase (cubic) at a pressure around 2.8 GPa. Ni₂MnGa alloy has the double possibility of phase transition under thermal effect and uniaxial stress.