A auto-loading firearm lockable manual safety mechanism operable to disable the firing control mechanism of the firearm. The firearm may include a frame, a pivotable hammer, and a trigger bar operably coupled to a pivotable trigger for cocking and releasing the hammer. In one embodiment, the trigger bar is movable between a firing position and standby position in which the firing mechanism is disabled. A rotary-operated camming member is provided that is engageable with the trigger bar. The camming member is operable to move the trigger bar between the firing and standby positions. In one embodiment, the camming member may be key-operated.