Selective laser melting (SLM) as an additive manufacturing (AM) route for the layer-upon-layer fusion of metallic powder beds was applied on a NiTi alloy along with two other states of a NiTi/1.5 wt% Nb nanocomposite, and NiTi-Nb eutectic powder mixtures. Initially, the SLM processing parameters were optimized to construct rectangular sound blocks from these materials with a theoretical density of >99.9%. Then, the microstructural characteristics of the processed materials were elaborated to reveal cellular nano-grain formation upon rapid cooling during SLM. Additionally, the distribution of Nb nanoparticles along the boundaries and eutectic phase transformations was analyzed. The functional performance of these materials was examined by undergoing miniature tensile testing at different temperatures along with nanoindentation experiments to measure the pseudoelasticity and the mechanical strength. As one of the leading objects, the effects of Nb nanocomposite fabrication and Nb-alloying through SLM layer-by-layer deposition on the strengthening and stability of NiTi alloy properties were studied.