A valve deactivator assembly (13) for an internal combustion engine, the assembly including a drive rocker arm (39) receiving cyclical motion from an engine push rod (23), and a driven rocker arm (41) which engages the engine poppet valve (29). The rocker arms are biased by a lost motion spring (49) to a position in which the rocker arms align to define a latching chamber (63), having a moveable latch member (65) disposed therein and biased by a spring (67) toward a latched position (FIG. 1). An electromagnetic actuator assembly (81) is disposed adjacent the rocker arms (39,41) and in response to an input signal (88), exerts a force on an actuation shaft (93) and an actuation beam (97) to move the latch member (65) toward its unlatched position (FIG. 3). The invention provides an effective, compact valve deactivator which can change quickly between the latched and unlatched conditions.