Field pea starch was thermally solubilized in water and subsequently ultrasonicated and then used to produce starch nanoparticles (SNPs) via a rapid nanoprecipitation method with the addition of the antisolvent (AS) ethanol into the starch solution (solvent, S). The spherical shape of SNPs with a small mean particle size was visualized by dynamic light scattering (DLS) and field emission-scanning electron microscopy (FE-SEM), which demonstrated a narrow size distribution (PSD) and good water dispersibility. Processing parameters, such as duration and amplitude of ultrasonication, AS/S ratio, starch concentration, separation and drying techniques, were investigated in relation to their effect on SNPs properties. There is an optimal AS/S ratio (1:1) and starch concentration (10 mg/mL) which gives rise to smaller SNPs with a narrower PSD. The formation of SNPs was found to follow a kinetically controlled nucleation-growth/aggregation mechanism in which amylose molecules formed the initial critical nuclei. The ultrasonication amplitude and separation and drying techniques significantly affected the size and morphology of SNPs. Moderate shear facilitated rapid starch aggregation and SNPs precipitation, enabling easy recovery by centrifugation and subsequent freeze drying. The freeze-dried SNPs were able to be dispersed quickly to form a SNP suspension in Milli-Q water. The dispersed SNPs showed good thermal stability in water and retained their particle characteristics at a temperature range of 25–60 °C. Further research exploring the potential of these SNPs as nutraceutical carriers for applications in both health and nutrition industries is warranted.