Shape-controlled LaNiO3 nanoparticles were prepared by modified hydrothermal and precipitation routes resulting in cubes, spheres, and rods. The solid-phase crystallization of LaNiO3 into its active catalyst form, Ni/La2O3, was found to be highly dependent on the shape and structure of the parent nanoparticle. Factors such as the crystallization pathway and Ni2+-ion depletion are considered as key factors influencing the final material. Catalysts derived from LaNiO3 spheres and rods were found to be free of carbon accumulation after 100 h of reforming, while those derived from cubes showed excessive carbon accumulation and signs of sintering. All three catalysts are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), and thermogravimetric analyses (TGA). The presence of defects, particularly stacking faults within the perovskite, may impact the reduction pathway and subsequent catalytic properties. Stable and active catalysts can therefore be designed and tuned by controlling the shape and structure of perovskite precursors.