A holster assembly for a handgun includes a double-locking system that comprises two distinct and independent locking devices. A first passive locking device is actuated by the weight of the gun, upon its insertion into the holster, and a second passive locking device is actuated by a spring. An active locking device is also provided that further secures the handgun to the holster to avoid inadvertent removal or discharge of the handgun. The active locking device is movable between a plurality of positions to provide varying degrees of securement for the handgun to the holster. The holster assembly further includes a height-regulating system to adjust the height of the assembly with respect to the user's body.