Wire Arc Additive Manufacturing (WAAM) is a method of Directed Energy Deposition (DED) technology that employs a metal wire and an electric arc as the heat source to melt the wire and build components layer by layer. Compared to other additive manufacturing methods, WAAM offers a significantly higher deposition rate, making it well suited for producing large scale components. The Gas Metal Arc Welding (GMAW) technique, with the Cold Metal Transfer (CMT) process, has been extensively adopted in WAAM due to its high reliability and cost effectiveness. Various materials have been explored using this method, including aluminium, titanium, magnesium alloys, and steels. This study was conducted to investigate how process parameters affect the microstructure and properties of High Strength Low Alloy (HSLA) steel, AristoRod 89, manufactured through WAAM. The primary objective was to determine optimal parameters that enhance both production efficiency and mechanical properties, while minimizing defects and material wastage with both economic and environmental threads. A total of 19 samples were fabricated by Wire Feed speed (WFS) (3.0–9.0 m/min) and Travel speed (TS) (4–12 mm/s) combinations. The experiments involved calculating energy input using arc logger data and compared with the properties with all samples. Vickers hardness test performed for both horizontal and vertical direction to identify hardness variation in different layers. Microscopic cross was also performed to identify internal defects and wall geometries. Where high energy input resulted in larger but less stable walls, while moderate parameter combinations produced more uniform and effective structures. The study found that the most effective parameter combinations (effectiveness over 73%) were achieved with WFS 3-4.5 m/min and TS 6–8 mm/s, balancing material utilization, geometry, and thermal stability. Hardness measurements showed a generally decrease with increasing energy input, higher hardness at the bottom layers due to faster cooling rates and hardness relatively reduce with height. Notably, among the 19 samples, sample no 5 and no 8 maintained relatively consistent hardness values horizontally. Defect analysis indicated that no lack of fusion or incomplete bonding occurred, due to appropriate overlap distances and sufficient energy input. Minor oxide inclusions were observed, particularly in the first layer. The results suggest that moderate settings, such as WFS 3 m/min and TS 6 mm/s or 8 mm/s, can provide a good balance of material utilization, structural integrity, and defect control. These findings offer valuable insights for build a defect free AristoRod 89 WAAM part