The sheet stacker (1) comprises a sheet conveyor arrangement (3), configured for feeding a plurality of sheets (C) and having a sheet discharge end (17), and a stacking bay (5). In the stacking bay sheets (C) delivered by the sheet conveyor arrangement (3) are formed into stacks (S). A stack conveyor (19) is provided in the stacking bay (5) and is movable in a conveyor direction (fl9) parallel to a sheet feeding direction (F), according to which the sheets (F) are fed from the sheet discharge end (17) onto the stack conveyor (19). The sheet discharge end (17) is configured and controlled such that it is gradually lifted during sheet stacking, in order to accommodate a growing stack (S) of sheets (C) being formed on the stack conveyor (19). A stop plate (37) is positioned in the stacking bay (5) above the stack conveyor (19) and in front of the sheet discharge end (17) of the sheet conveyor arrangement (3). The stop plate (37) is configured and controlled to be gradually lifted from the stack conveyor (19) as the sheet stack (S) grows, to be withdrawn upon completion of the stack (S) thus allowing removal of the stack in an evacuation direction (fE) substantially parallel to the conveyor direction (fl9), and to be lowered towards the stack conveyor (19) again.