Plasma arc welding was implemented for additive manufacturing 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 arc length, nozzle size, shielding gas flow rates, 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. The multiple-layer deposited with optimized parameters shows complete fusion without visible voids. However, some interface separations were found due to the minor surface oxidation in between layers. Equiaxed-to-columnar grain structure was also observed along the deposition direction where molybdenum carbides were present. Further hardness test on the multiple-layer sample shows a superior isotropic hardness (HV 218) when compared with wrought Hastelloy X (HV 179). Multiple-layer depositing techniques were satisfactorily developed to prevent overheating.