The influence of first-row transition metals on structural, electronic, and nonlinear optical (NLO) properties of aluminum phosphide (Al12P12) inorganic fullerene is investigated through DFT methods. The designed [email protected]12P12 composites are thermodynamically quite stable. Frontier orbital analysis revealed that HOMO–LUMO energy gap of Al12P12 nanocluster is fairly reduced in the presence of transition metals which is mainly attributed to the formation of new high HOMO energy levels due to excess electrons. Based on the NBO analysis, the charge is transferred from transition metal to the Al12P12 nanocluster. The calculated polarizability (αo) and the first hyperpolarizability (βo) values indicated that nonlinear optical response is remarkably enhanced under the influence of first-row transition metals. These [email protected]12P12 composites possess giant first hyperpolarizabilities in the range of 3.1×102–5.9×106 au. This study may provide valuable insights for the designing of new high-performance materials for optoelectronic devices.