In accordance with the present disclosure, a system and method for Modular, Locking Headrail-Retention Mechanism is described. The module, locking headrail-retention mechanism may, in certain embodiments be separate from a headrail, and insertable into at least one end of the headrail. In other embodiment, the locking headrail-retention mechanism may be manufactured as part of the headrail. The locking headrail-retention mechanism may comprise a cylindrical housing and a first cam disposed within the cylindrical housing. The locking headrail-retention mechanism may also include a retention plate proximate one end of the cylindrical housing and axially aligned with the first cam. A biasing member may be disposed within the cylindrical housing, and may impart an axial force on the first cam. The first cam may be operable to selectively prevent the axial force from being imparted on the retention plate.