Ice cores from Antarctica record temperature and atmospheric carbon dioxide variations over the past six glacial cycles1, 2. Yet concomitant records of sea-level fluctuations—needed to reveal rates and magnitudes of ice-volume change that provide context to projections for the future3, 4, 5, 6, 7, 8, 9—remain elusive. Reconstructions indicate fast rates of sea-level rise up to 5 cm yr-1 during glacial terminations10, and 1–2 cm yr-1 during interglacials11, 12 and within the past glacial cycle13. However, little is known about the total long-term sea-level rise in equilibration to warming. Here we present a sea-level record for the past 520,000 years based on stable oxygen isotope analyses of planktonic foraminifera and bulk sediments from the Red Sea. Our record reveals a strong correlation on multi-millennial timescales between global sea level and Antarctic temperature1, which is related to global temperature6, 7. On the basis of this correlation, we estimate sea level for the Middle Pliocene epoch (3.0–3.5 Myr ago)—a period with near-modern CO2 levels—at 255 m above present, which is validated by independent sea-level data6, 14, 15, 16. Our results imply that even stabilization at today's CO2 levels may cause sea-level rise over several millennia that by far exceeds existing long-term projections3. ---