Wave-induced longshore sediment transport is a major basinal process that reworks fluvial sediment supply along a delta–shoreface depositional system. However, the effects of the variable counterbalance between supply and wave reworking have not been sufficiently acknowledged in understanding paleoshoreline evolution and stratigraphic concepts such as sequence stratigraphy and autostratigraphy. With a numerical shoreline model, we quantify the relation between wave-induced longshore sediment transport and shoreline orientation under conditions of steady sea level. A case study of the Po delta–shoreface system reveals that a decrease in delta progradation rate can in part be considered as an autogenic response to steady wave conditions offshore. Long-term wave-induced transport can be quantified by the volume of sediment redistribution. As such, we propose a revised definition of accommodation space by integrating the effect of wave-induced longshore transport. Wave-induced longshore sediment transport has a significant impact on progradation of deltaic and adjacent shoreface shorelines, and needs to be considered while interpreting shallow-marine stratigraphy.