A foldable firearm sight assembly including a leaf spring is disclosed. The disclosed assembly may include a base, a sight arm, and a leaf spring. The base of the sight assembly may be configured to attach to a firearm rail using, for example, a clamp bracket and a clamp bolt. The sight arm may be rotationally coupled to the base, and the leaf spring may be positioned between the base and the sight arm. When installed in the sight assembly, the leaf spring may be deflected and may apply a biasing force to the sight arm, causing the sight arm to favor either a deployed or stowed (undeployed) position. The sight arm may be lockable in stowed and/or deployed positions using a tooth and aperture configuration. In such lockable cases, the arm may be unlocked/released by manually depressing an end of leaf spring.