||The important features of nitrides materials include extreme hardness, high thermal conductivities, and make them as strategic material system for device applications at high pressure and temperature. The purpose of the present study is to predict novel ternary III–V alloys based on the TlN compound. We present and analyse first the important features of pure TlN before handling the complete contribution regarding the predictive alloy Ga1−xTlxN. From the obtained results we notice the inverted band gap in TlN, which reflects a semi-metallic character and a strong charge transfer towards the nitrogen atom. For Ga1−xTlxN alloys, the optical band gap bowing (i.e., the nonlinearity noticed in the variation of the alloy as a function of the amount of concentration x) is found to be strong and composition dependent following the same tendency of the other highly mismatched III–V alloys, where the composition induces disorder in bond lengths.