A detailed theoretical study is carried out to explore the effects of oxynitrides while considering cubic bismuth aluminate with different concentrations of nitrogen from x = 0 to x = 3. This report evaluates the structural, total, and partial densities of states (TDOS/PDOS), modification in the electronic band gap, and optical properties due to the inclusion of nitrogen based on the ab-initio method with generalized gradient approximation (GGA) as implemented in CAmbridge Serial Total Energy Package (CASTEP). All the structural parameters of BiAlO3 agree well with earlier reported values. A change in the perfect cubic structure of BiAlN3 is observed for 100% nitrogen substitution. Pure BiAlO3 is found to have an indirect band gap of 1.487 eV along with the high symmetry points between the 2p orbital of O and the 6p orbital of Bi. Reduction in band gap is reported with increasing concentration of N, due to which the material tends to behave like a conductor at a point and then the electronic band gap begins to increase as the impurity concentration increase passes this point, mainly as a consequence of the nonlinear band gap dependence on the composition of the material. A density of state (DOS) study concludes the existence of covalent bonding between O–Bi and O–Al with strong hybridization. There is an increase in the contribution of these orbitals informing energy states as the nitrogen atoms successively add up in the material BiAlO3–x N x . The BiAlN3 compound, having a perfect cubic structure, is reported here for the first time. Numerous optical characteristics have been studied comparatively at different concentrations of N, with the report that BiAlN3 has a higher value of the refractive index than bismuth aluminate, with amended optical behavior. The trend of these optical properties with respect to nitrogen concentration is also demonstrated. We propose this cubic phase of BiAlN3 as a potential material for optoelectronic applications.