A narrow profile surgical ligation clip has two legs with clamping surfaces joined by a hinge near the proximal ends, allowing the clip to reversibly open and close. A locking mechanism is proximal to the hinge to bias or lock the clip closed, including first and second jaw structures spaced on opposite sides of a longitudinal axis of the clip thereby defining a locking space therebetween. In one embodiment, a wedge or buttress body moves by application of an external force applied to a proximal end of the clip towards the hinge to move into the locking space such that one or more outer surfaces or projections of portions of the body fit into or abut against complementary surfaces or other parts of the locking mechanism or clip assembly to bias or lock the clip in a closed position and provide additional closing force to the inner clamping surfaces.