A beverage container closure or lid adapted for closing an open end of a beverage container. The lid is couplable to the beverage container and includes a selectively openable stopper that when closed, creates a fluid-tight seal between the beverage container and the environment. The stopper may be opened by pressing a button disposed on a side of the beverage container closure. The stopper is subsequently automatically closed when the button is released. Thus, the user may open and close the beverage container closure using a single hand without the need to remove the beverage container closure from the beverage container. The beverage container closure includes an actuating lever configured to press the button when a user applies a force to the lever. By utilizing the mechanical advantage provided by the lever, a user is able to selectively open and close the stopper using a relatively low amount of force.