Evidence from terrestrial, glacial, and global climate model reconstructions suggests that a sea-level jump caused by meltwater release was associated with the triggering of the 8.2 ka cooling event. However, there has been no direct measurement of this jump using precise sea-level data. In addition, the chronology of the meltwater pulse is based on marine data with limited dating accuracy. The most plausible mechanism for triggering the cooling event is the sudden, possibly multistaged drainage of the Laurentide proglacial Lakes Agassiz and Ojibway through the Hudson Strait into the North Atlantic ca. 8470 ± 300 yr ago. Here we show with detailed sea-level data from Rotterdam, Netherlands, that the sea-level rise commenced 8450 ± 44 yr ago. Our timing considerably narrows the existing age of this drainage event and provides support for the hypothesis of a double-staged lake drainage. The jump in sea level reached a local magnitude of 2.11 ± 0.89 m within 200 yr, in addition to the ongoing background relative sea-level rise (1.95 ± 0.74 m). This magnitude, observed at considerable distance from the release site, points to a global-averaged eustatic sea-level jump that is double the size of previous estimates (3.0 ± 1.2 m versus 0.4–1.4 m). The discrepancy suggests either a coeval Antarctic contribution or, more likely, a previous underestimate of the total American lake drainage.