To assist in the sustainable management of water resources, a groundwater model of the shallow groundwater in the Plaine du Nord–Massacre transboundary aquifer system was developed. The Plaine du Nord–Massacre Aquifer is one of the largest aquifer systems of Haiti, supposedly bearing a high potential for water supply and irrigation. The shallower part is already tapped by hundreds of domestic wells and hand-pumped public and private boreholes. In the framework of the AVANSE project (Appui à la Valorisation du Potentiel Agricole du Nord, pour la Sécurité Économique et Environnementale), a USAID funded project aiming at developing sustainable agriculture in the region, a groundwater model was built to assist in decision making. The finite-difference-based MARTHE software was used for the model. Due to the lack of monitoring data, the calibration of the model could only be carried out under steady-state hydraulic conditions. It should thus be considered as a first step towards a better characterisation of the aquifer’s potential. However, the model computed a groundwater balance at the scale of the aquifer showing that significant water resources can be easily mobilized if one carefully manages to rule out local operational difficulties. The simulated groundwater drawdowns using transient simulation of irrigation scenarios are pluri-metric, reaching 6–7 m. New irrigation wells must be deeper than the current average depth of wells to support agricultural development projects.