Global Positioning System measurements and high‐resolution offshore seismic data within the transform Caribbean–North American plate boundary in southern Haiti, Greater Antilles, show 6–7 mm/yr of plate boundary‐normal shortening within a crustal sliver bounded to the south by the Enriquillo left‐lateral strike‐slip fault and to the north by a south‐dipping reverse fault system offshore the northern coast of the Southern Peninsula of Haiti. This overlooked fault system, which we name “Jérémie–Malpasse” (JM), marks the overthrusting of the Cretaceous oceanic crust of the Caribbean basin of the Southern Peninsula over accreted terranes of island arc crust to the north. Geological and geodetic data are consistent with a tectonic model that reconciles recent observations of plate boundary‐perpendicular shortening with ample geological evidence for purely strike‐slip motion on the Enriquillo fault. This model also provides a framework to interpret the 2010 7.0 and 2021 7.2 earthquakes in southern Haiti, whose oblique slip mechanisms are indicative of a localized transpressional strain regime. These findings imply that regional seismic hazard maps must be updated to account for both the existence of the ∼350 km long JM fault system and for the possibility that future earthquakes in southern Haiti may occur on nonvertical faults with a significant component of reverse slip.