Locking line capture devices for unmanned aircraft, and associated systems and methods are disclosed herein. A representative system includes a line capture body having a line slot with an open end and closed end, and a retainer positioned proximate the line slot and movable between first position in which the retainer blocks access to the line slot and a second position in which the retainer allows access to the line slot. A locking device is operably coupled between the capture body and the retainer and is movable between an unlocked position to allow movement of the retainer between the first and second positions, and a locked position to block such movement. A release device is operably coupled to the locking device and movable between a secured position with the locking device secured in the locked position, and a released position with the locking device movable between the locked and unlocked positions.