A material with strong thermal stability and mechanical resilience, specifically in thin film form, is necessary for any device application. Before a material’s synthesis or any device’s realization, density functional theory provides early access to understanding various characteristics and related processes, including optical, magnetic, thermodynamic, and electrical transport. Numerous applications, such as spintronics, thermoelectrics, shape memory, spin injection, topological insulators, etc., have been investigated using Heusler alloys. In this work, by performing ab-initio calculations using Quantum Espresso formalism, we examined the thermodynamic stability and electronic structure of CoNiSi Heusler alloys. We have predicted a stable phase for this alloy by minimizing the ground state energy. The lack of a gap at the Fermi level for both spin-up and spin-down bands indicates the absence of a half-metallic character in this alloy. The occurrence of positive phonon frequencies ensures thermodynamic stability, which is also confirmed by the Born-Huang criterion established by the elastic constants.