The Madagascar Plover Charadrius thoracicus is a threatened wader endemic to Madagascar. We report the first detailed study of its distribution and breeding ecology. Madagascar Plovers breed on the west coast of Madagascar between the Mahavavy delta in the north and Fort-Dauphin in the south-east. Between 2002 and 2005, we found a total of 149 nests concentrated at two sites: Lake Tsimanampetsotsa (108 nests), an alkaline inland lake in the south, and Marambitsy Bay (24 nests) on the north-west. Nesting was observed between August and May, with peak activity between December and April. We followed the success of 74 nests from egg-laying to chick fledging. Hatching and fledging success were both low (22.9% and 41.4%, respectively, using the Mayfield method). Overall breeding success was also low and only 9.5% of nests produced fledged chicks. The effects of this low breeding success are compounded by the specific habitat requirements of the plover and its limited dispersal. Using these data, we constructed three population projections, all of which predict rapid population decline. The Madagascar Plover is currently classified as Vulnerable by the IUCN but, given its low breeding success and bleak population trajectories, a review of this status may soon be necessary.