Contemporary robotic applications, with recent advancements in the integration of intelligence, are distinguished by the enhanced interactions with both environments and humans, necessitating diverse operational capabilities. Specifically, certain applications demand high torque for intensive tasks, while others require high compliance to ensure safety and comfort during interaction. However, while both have been addressed to some extent through actuator design, these two sets of requirements are often mutually exclusive due to opposing design principles. This paper presents a novel design of a switchable-mode elastic actuator that can alternate between high-torque and high-compliance modes by fixing and relaxing the planetary wheel’s internal gear ring, thus meeting the dual requirements of advanced robotic systems. Experimental results confirm the actuator’s primary capability for both modes. This innovation holds significant potential for broadening the functional versatility of robots in complex, interactive applications.