A gate valve actuator including a stem that is movable linearly in an actuator housing connectable to the gate valve. The stem acts on the gate valve to shift the gate valve between open and closed positions, respectively. The stem is driven by a motor in a first direction into a steady state operation position. In the position the stem is biased in a second opposite direction towards a shutdown position by a spring member acting on the stem. A trigger mechanism is arranged for holding the spring member in a compressed state. The trigger mechanism includes an electrically controllable trigger that is arranged for release of the spring member in result of de-energizing the electrically controlled trigger. A method for shifting a gate valve between a steady state operation mode and a shutdown mode utilizing the gate valve actuator.