Abstract Greenland ice sheet mass loss to the marine environment occurs by some combination of iceberg calving and underwater melting (referred to here as marine ice loss, LM). This study quantifies the relation between LM and meltwater runoff (R) at the ice sheet scale. A theoretical basis is presented explaining how variability in R can be expected to govern much of the LM variability over annual to decadal time scales. It is found that R enhances LM through three processes: 1) increased glacier discharge by ice warming–softening and basal lubrication–sliding; 2) increased calving susceptibility through undercutting glacier front geometry and reducing ice integrity; and 3) increased underwater melting from forcing marine convection. Applying a semiempirical LM f(R) parameterization to a surface mass balance reconstruction enables total ice sheet mass budget closure over the 1840–2010 period. The estimated cumulative 171-yr net ice sheet sea level contribution is 25 ± 10 mm, the rise punctuated by periods of ice sheet net mass gain (sea level drawdown) (1893–1900, 1938–47, and 1972–98). The sea level contribution accelerated at 27.6 mm yr−1 century−1 over the entire reconstruction, reaching a peak sea level rise contribution of 6.1 mm decade−1 during 2002–10.