The Arctic Oscillation (AO), the dominant mode of extratropical Northern Hemisphere circulation, is known to influence midlatitude climate variability, but its impacts on tropical rainfall–particularly over the Maritime Continent (MC)–remain unclear. Here, we examine the influence of the boreal spring AO on midsummer (July–August) MC precipitation during the period 1979–2023. The results reveal a significant negative relationship between midsummer MC precipitation and the preceding March–April AO. Further examination identifies a physical mechanism linking the two: during the negative phase of the March–April AO, atmosphere–ocean interactions generate warm sea surface temperature (SST) anomalies in the North Atlantic that persist from March to August. These mid–latitude SST anomalies in the North Atlantic trigger an atmospheric wave train that propagates from the North Atlantic to the North Pacific, ultimately inducing pronounced westerly wind anomalies in the upper troposphere and easterly wind anomalies in the lower troposphere over the tropical western Pacific in July–August. This circulation pattern enhances vertical wind shear, promoting anomalous ascent via dynamic pumping and increasing rainfall. Simulations using the Community Atmosphere Model (CAM5.3) further validate the proposed mechanism.