Wire Arc Additive Manufacturing (WAAM) is a metal 3D printing method that enables the manufacture of geometrically complex metal components with lower cost and higher deposition rates relative to other metal 3D printing methods. Although numerous studies have recently been conducted on the mechanical properties and physical characteristics of WAAM steel elements, there are still uncertainties regarding the selection of the appropriate process parameters when certain mechanical or geometric characteristics are required. To address this shortcoming, a comprehensive experimental programme has been conducted to investigate the influence of the key process parameters on the weld quality and geometric properties of WAAM wall elements. Following an investigation matrix approach, the present study was carried out in two stages. Fifty-six combinations of wire feed speeds and travel speeds covering a big range of heat inputs were used to produce short WAAM walls. The walls were classified according to the weld quality and their average thickness and average layer height were determined. Subsequently, to investigate the sensitivity of the average layer height to the number of printed layers, fifteen taller WAAM walls were printed based on the high quality printing strategies from the initial short wall investigation. From this investigation useful conclusions are obtained regarding the influence of heat input during the WAAM process on the geometric and mechanical properties of the 3D-printed components.