The CoNiGa ternary system has recently emerged as a promising alternative to currently used high temperature Shape Memory Alloys (SMAs), with possible applications in the aerospace and automotive industries. In this work, we use thermodynamic modeling based on the CALPHAD approach to investigate the thermodynamic properties, phase stability and shape memory properties of these alloys. The thermodynamic model parameters have been obtained by fitting experimental and ab initio data. The stability of the β phase at high temperatures was enforced accurately by remodeling the CoGa system. Also, the phase stabilities of Ni5Ga3Ni5Ga3(δ)(δ) and Ni13Ga9Ni13Ga9(ε)(ε) were determined as they are known to cause detrimental effects in the ternary at low temperatures.