Nitinol (NiTi) alloys have a lot of potential applications in the medical, aerospace, and energy sectors, due to their superelasticity and shape memory effect (SME), low stiffness, good biocompatibility, and high corrosion resistance. However, their poor machinability has limited the ability to process NiTi, especially into complex shapes. Recently, the Laser Powder Bed Fusion (L-PBF) technique has been found effective to process complex shapes in metallic systems as well as providing a high degree of sustainability. The phase transformations which enable functional properties in NiTi are highly sensitive to the L-PBF processing conditions. This thesis explores the functional and material behaviour of NiTi in the specific design space of L-PBF process parameters in the as-fabricated condition; and develop an understanding how the L-PBF process can be altered to attain tailored properties. Porosity is a common phenomenon and a major defect entity in L-PBF processed parts. A finite element model was used to correlate the macroscale effect of porosity and microscale effect of martensitic phase evolution with structural stiffness, dissipated energies, and damping properties. Experimental investigations were also performed following a systematic variation of L-PBF process parameters using different build orientations. The effect of these factors on porosity levels, phase transformations, transition enthalpies and thermal expansion characteristics were characterised and reported. The microhardness, impact and mechanical strength, and strain recovery of the L-PBF processed NiTi were investigated and presented alongside a full-field strain analysis. The detwinning mechanisms and local strain field effects were explored at submicron levels, which was then correlated with the SME capabilities of L-PBF samples. Several microstructural characterisation techniques were utilised to identify and elucidate the reported findings and present how the L-PBF parameters and build orientations control the SME of NiTi.