The catastrophic demise of the Aral Sea in the late twentieth century has stimulated significant international efforts to understand the geological, hydrological, and climatological controls on lake level at timescales ranging from years to millennia. Here we extend this time range to the Late Pleistocene with sedimentological, chronological and paleontological results from a core that dates from ca. 17.6 kyr cal BP. To our knowledge, this Aral Sea core (B-05-2009) is the oldest directly-dated sediment record with multiple late Pleistocene 14C dates currently available from the region. The core shows that the modern Aral Sea formed at least as early as the end of the Last Glacial Maximum. The main source of water was most likely glacial meltwater from the Tian Shan, Pamir, and other distant mountain systems in the modern day Aral Sea watershed, carried by the Syr Darya and Amu Darya rivers. The Late Pleistocene section of the core contains ostracods and foraminifera throughout, providing evidence that the lake supported life since its inception. Our chronology suggests a relatively high average sedimentation rate at the onset of lake development, and a significant sedimentation hiatus around the time of the Pleistocene/Holocene boundary.