Abstract The North Pacific eastern subtropical mode water (NPESTMW) connects the subtropics and tropics, influencing climate variability on interannual to decadal timescales. Using eight decades of ocean reanalysis, we show that the 11‐year solar‐cycle robustly modulates NPESTMW volume. NPESTMW formation is suppressed 1–2 years after solar maxima: high solar activity deepens the Aleutian Low, reducing wintertime wind stress and surface heat loss, producing shallower mixed layers. Concurrently, cyclonic wind‐stress anomalies drive Ekman upwelling, further inhibiting subduction. Conversely, solar minima favor mixed layer deepening, Ekman downwelling, and thus enhanced subduction, increasing NPESTMW volume. Solar‐forcing‐only CMIP6 experiments reproduce these responses, confirming solar variability as a causal driver. The Atlantic Multidecadal Oscillation gates this solar–mode‐water relationship, amplifying solar‐cycle expression during warm phases and explaining the enhanced solar imprint on decadal climate since the 1990s. These results reveal a novel pathway linking solar forcing to decadal climate predictability through subsurface ocean memory.