Plasma arc welding (PAW) was implemented for additive manufacturing (AM) of Hastelloy X wire due to its potential to produce thin-wall structures for a high-temperature resistance of Hastelloy X. Single-layer beads were deposited to study and optimize the effects of eight process parameters (arc length, nozzle size, built-in and trailing shielding gas flow rate, wire feed rate, travel speed, current, and linear energy density). In the meantime, an additional trailing shielding mechanism was introduced to reduce surface oxidation while maintaining acceptable geometry for multiple-layer deposition. A multiple regression method was used to determine the influence of these parameters on the extent of oxidation, geometry, height and width of bead. The optimized parameters were then used for multiple-layer depositions where complete fusion without visible voids was achieved. However, some interface separations were found due to the minor surface oxidation between layers. Equiaxed-to-columnar grain structure was also observed along the deposition direction where molybdenum carbides were present. The final samples were further evaluated by hardness test. A superior isotropic hardness (HV 218) was achieved on the multiple-layer sample when compared with wrought Hastelloy X (HV 179). Multiple-layer depositing techniques were satisfactorily developed in this study. The optimized PAW process was proven to prevent overheating during starting and ending portion of the deposition. Heat reduction for each successive layer was also determined to produce a wall structure