This work studied the effect of solution heat treatment on the microstructure and properties of the Al–Cu alloy fabricated by wire arc additive manufacturing (WAAM), and focused on the influence of porosity and second phase evolution on the tensile properties and fatigue resistance of the alloy. The results show that with solution heat treatment at 530 °C for 1h, Al–Cu alloy fabricated by WAAM with low porosity (2.4 %) and high peak hardness (148.2 HV) can be obtained. Higher solution temperatures significantly increased the porosity, and extending the solution time caused the problems of increased porosity, micropore growth, microcracks as well as cavity. Influence of porosity on fatigue resistance is more significant than that on tensile properties. The results of tensile tests suggest that the effect of porosity on the strength of T6-treated alloy is limited and much smaller than that of the precipitation strengthening induced by precipitates, while the results of the fatigue crack propagation tests imply that porosity plays the dominant role in the fatigue crack propagation behaviors of the T6-treated alloy.