Additive manufacturing (AM) rapidly expands to all research areas due to its multiple advantages, such as the freedom and flexibility in achieving any geometry. Using AM as a fabrication technique, the design process has almost no limitations, blending considerably well with the irregular geometries that may result from topology optimization. Yet, in practice the application of AM together with topologically optimized geometries is not as straightforward. In this research, a hollow square t-joint is used as a case study to investigate and understand the difficulties in the design and manufacturing of steel parts using wire arc additive manufacturing (WAAM). The case study showcases from the application of two optimization methods with various parameters to find an optimal geometry; numerical analysis (FEM) on non-optimized and optimized models; a procedure called “re-engineering” that adjusts the optimized geometry to structure efficiency and AM effectiveness; dynamic slicing and path planning; an adjustment of the welding parameters to enhance the material properties and accuracy of the final specimens; and experimental assessments on non-optimized and optimized printed t-joints to validate the entire process. The application of this process allowed the manufacture of a complex optimized geometry, which have more resistance than the non-optimized T-joint.