Observations of ocean-terminating outlet glaciers in Greenland and West Antarctica¹⁻⁶ indicate that their contribution to sea level is accelerating as a result of increased velocity, thinning and retreat⁷⁻¹¹. Thinning has also been reported along the margin of the much larger East Antarctic ice sheet¹, but whether glaciers are advancing or retreating there is largely unknown, and there has been no attempt to place such changes in the context of localized mass loss⁷’⁹ or climatic or oceanic forcing. Here we present multidecadal trends in the terminus position of 175 ocean-terminating outlet glaciers along 5,400 kilometres of the margin of the East Antarctic ice sheet, and reveal widespread and synchronous changes. Despite large fluctuations between glaciers—linked to their size—three epochal patterns emerged: 63 per cent of glaciers retreated from 1974 to 1990, 72 per cent advanced from 1990 to 2000, and 58 per cent advanced from 2000 to 2010. These trends were most pronounced along the warmer western South Pacific coast, whereas glaciers along the cooler Ross Sea coast experienced no significant changes. We find that glacier change along the Pacific coast is consistent with a rapid and coherent response to air temperature and sea-ice trends, linked through the dominant mode of atmospheric variability (the Southern Annular Mode). We conclude that parts of the world’s largest ice sheet may be more vulnerable to external forcing than recognized previously.