This study investigates the mechanical and microstructural behavior of AISI 304 steel welds produced using the CO₂ laser welding process. The focus is on understanding the effects of different welding conditions on 2 mm thick steel sheets. The welds were performed under three conditions: autogenous welding without root opening, welding with a 1 mm root opening using filler metal, and welding with filler metal but without root opening. The joints were analyzed using scanning electron microscopy (SEM), microhardness testing, uniaxial fatigue testing, and subsequent fractographic examination. The microstructural analysis revealed a significant presence of pores in the autogenous welds and predominant formation of delta ferrite and lathy ferrite phases across all conditions. In terms of mechanical performance, autogenous welds exhibited fractures in the base material, while welds using filler metal showed fractures near the weld metal. Despite noticeable differences in the mean fatigue resistance, the autogenous welds and those with filler metal but without root opening demonstrated a higher number of cycles to failure.