The alloying effect of three elements, namely Al, Cr and Zn, on the Pt site of L1₂ Cu₃Pt phase was investigated using DFT (density functional theory) based first-principle calculations in attempt to stabilize it in the form of L1₂ Cu₃Pt_1-xY_x ternary alloy. On the basis of phase stability and elastic properties, the substitution behaviour of all three alloying elements were compared with properties of thermodynamically sluggish Cu₃Pt phase. The calculated heats of formation reveal that the thermodynamic phase stability is gradually enhanced with increasing content of aluminium alloying and diminished with increasing content of zinc and chromium. In this current work, the stress-strain approach was used according to Hooke’s law to calculate elastic properties such as elastic constants, Young’s modulus E, shear modulus G, bulk modulus B and Poisson’s ratio v, as they play an important role to investigate the resulting mechanical properties. The calculated results show that alloying with all three elements maintains the mechanical stability criteria of cubic crystals. Considered L1₂ Cu₃Pt_1-xY_x ternary alloys exhibit the most ductile character with Al addition, followed by Cr, whereas introduction of Zn yielded lowest ductility at higher compositions.