Research on miniature deep-sea robots is an emerging field focused on the development of deployable, compact devices capable of interacting with the unique environments and organisms of the deep ocean. In this study, we present a design strategy for a centimeter-scale deep-sea soft actuator, weighing 16 grams, that incorporates bistable chiral metamaterials and tube-sealed shape memory alloys. According to our design, the increased modulus induced by the hydrostatic pressure was used to achieve a higher snapping velocity of the bistable chiral unit, thus lifting the actuator’s performance. We showed that the actuator can produce undistorted cyclic motions at various depths in the deep sea. Subsequently, we developed an untethered miniature deep-sea robot that is capable of multimodal locomotion by repurposing its legs and fins. To validate the robot’s performance, this miniature robot was deployed from deep-sea crewed submersibles, performing swimming, gliding, morphing, and crawling in the Haima Cold Seep (1380-meter depth) and the Mariana Trench (10,600-meter depth); it was then retrieved by the submersible fully intact. The actuation module design enabled the robot to perform comparably in the Haima Cold Seep and laboratory aquarium conditions (atmospheric pressure). Additionally, we developed a wearable soft gripper based on the same metamaterial design strategy to facilitate safe deep-sea operations, ranging from soft-specimen collection to heavy-object manipulation (~3400-meter depth). This study offers design insights into creating next-generation miniature deep-sea actuators and robots, paving the way for future exploration and interaction with deep-sea ecosystems.