Embodiments of a cabin outflow valve having one or more laterally-tapered sealing surfaces are provided, as are cabin pressure controls system including cabin outflow valves. In one embodiment, the cabin outflow valve includes a frame and a first door, which is pivotally coupled to the frame and which is rotated by an actuator between open and closed positions. The first door includes, in turn, a torque input point at which the actuator applies a closing force when rotating the first door into a closed position. A laterally-tapered sealing surface extends along a lateral axis of the cabin outflow valve and has a profile height decreasing with increasing proximity to the torque input point. The laterally-tapered sealing surface helps to ensure the formation of a complete lateral seal when in the first door is rotated into the closed position to significantly reduce or eliminate leakage through the cabin outflow valve.