A thin wall of well-formed dense 2Cr13 martensitic stainless steel was successfully fabricated by wire arc additive manufacturing (WAAM). Heterogeneous distributions of the hardness and microstructure were found in the wall consisting of 20 layers along the building direction. The hardness profile of the thin wall mainly depended on the degree of tempering of the martensite. Based on the simulated and tested thermal history, the inter-pass temperature was lower than the martensitic transformation start (Ms) temperature in the first 10 layers. The thermal effect of the subsequent passes partially tempered the quenched martensite formed in the previous pass during cooling. By contrast, the inter-pass temperature was greater than the Ms temperature in the last 10 layers. The martensitic transformation mainly occurred after the final pass, resulting in a relatively homogeneous microstructure. This study suggests that the inter-pass temperature is a dominant factor in controlling the microstructural evolution during the WAAM of 2Cr13 martensitic stainless steel.