Although the 12 January 2010 Haiti earthquake was one of the deadliest earthquakes in history, it left no clear geological evidence of rupture on land. As a tectonic event, the earthquake was complex; even the faults involved remain unclear. Using geophysical and coring data, we document direct evidence of the sedimentation generated by the catastrophic 12 January 2010 earthquake offshore. These studies document submarine paleoseismology methods that can be used for assessing seismic risk in this and other tectonic settings such as the California San Andreas fault, where deeper buried blind thrusts may exist. Shaking by the 12 January main shock triggered sediment failures and turbidity currents from coastal sources to deep-water sinks. An ∼0.05 km3 turbidite was deposited in the Canal du Sud basin (1750 m water depth) over 50 km2. Almost 2 months after the main shock, a 600-m-thick sediment plume was still present in the lowermost water column at this location. The turbidite was time correlated to the 12 January earthquake by the excess 234Th in the sediments. With a half-life of 24 days, its presence documents an influx of terrigenous sediment mixing with marine sources derived from the basin slopes. This turbidite, and older ones observed beneath it, displays complex cross-bedded and fining-upward stratigraphy indicative of long waves and seiche oscillations that are consistent with locally reported tsunamis. This 12 January sedimentary record highlights the potential for submarine paleoseismology to unravel the seismic history of continental transform boundaries such as the Enriquillo–Plantain Garden fault in the Dominican Republic, Haiti, and Jamaica, as well as other tectonic settings where no clear land-based evidence for a rupture exists.