The deposition of sapropels in the eastern Mediterranean Sea is thought to occur during intervals of intensified African monsoon and increased precipitation in the Mediterranean borderlands. Speleothem and pollen records, however, reveal conflicting evidence for a Mediterranean-wide precipitation increase, suggesting that seasonal changes in the hydrological regime may be important. Using a multiproxy record, we present the first independent evidence for seasonality of precipitation during the early Last Interglacial (ca. 130–119 ka) from the Tenaghi Philippon peatland in northeast Greece. During the early part of the interglacial, mineralogical, macrofossil, and pollen records from the same core show a shift from mire to lacustrine conditions simultaneous with an expansion of sclerophyllous vegetation and the presence of acicular aragonite, indicating the onset of highly evaporative summer conditions. This indicates enhanced seasonality of precipitation and reconciles the apparent incongruity between Mediterranean pollen and speleothem records. It also provides evidence for significantly increased winter precipitation coeval with the deposition of sapropel S5, one of the most prominent sapropels of the Pleistocene. We suggest that in addition to the summer African monsoon component, increased winter precipitation from the northern Mediterranean borderlands may have contributed to maintaining reduced surface-water salinities in the Mediterranean Sea over the entire year.