Abstract: Wire arc additive manufacturing (WAAM) presents a promising approach for fabricating medium-to-large austenitic stainless steel components, which are essential in industries like aerospace, pressure vessels, and heat exchangers. This research examines the microstructural characteristics and tensile behaviour of SS308L manufactured via the gas metal arc welding-based WAAM (WAAM 308L) process. Tensile tests were conducted at room temperature (RT, 25°C), 300°C, and 600°C in as-built conditions. The microstructure consists primarily of austenite grains with retained δ-ferrite phases distributed within the austenitic matrix. The ferrite fraction, in terms of ferrite number (FN), ranged between 2.30 and 4.80 along the build direction from top to bottom. The ferrite fraction in the middle region is 3.60 FN. Tensile strength was higher in the horizontal oriented samples (WAAM 308L-H), while ductility was higher in the vertical ones. Tensile results show a gradual reduction in strength with increasing test temperature, in which significant dynamic strain aging (DSA) is observed at 600°C. The variation in serration behavior between the vertical and horizontal specimens may be attributed to microstructural differences arising from the build orientation. The yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of WAAM 308L at 600°C were (240 ± 10) MPa, (442 ± 16) MPa, and (54 ± 2.00)%, respectively, in the horizontal orientation (WAAM 308L-H), and (248 ± 9) MPa, (412 ± 19) MPa, and (75 ± 2.80)%, respectively, in the vertical orientation (WAAM 308L-V). Fracture surfaces revealed a transition from ductile dimple fracture at RT and 300°C to a mixed ductile–brittle failure with intergranular facets at 600°C. The research explores the applicability and constraints of WAAM-produced 308L stainless steel in high-temperature conditions, offering crucial insights for its use in thermally resistant structural and industrial components.