<p>In robotic hands, the thumb plays a crucial role due to its ability to perform opposition against the other fingers. The thumb typically performs three motions: opposition/reposition, abduction/adduction, and flexion/extension. However, when using underactuated mechanisms, certain motions are restricted to reduce the number of actuators. This study proposes a design that expands the workspace of the thumb, which is otherwise limited by such constraints. The proposed mechanism enables sequential translational and rotational movements in the thumb’s opposition/reposition motion using a single actuator, where the thumb first translates and then rotates to complete the movement. The robotic hand is composed of five fingers: the thumb is actuated by two actuators to perform opposition/reposition and flexion/extension, while each of the remaining four fingers is driven by a single actuator for flexion/extension. The system is actuated using linear actuators and a linkage mechanism, and the resulting joint motions are described with respect to actuator inputs. The workspace of the hand is analyzed and compared for cases with and without translational motion in the thumb. The effectiveness of the expanded workspace is experimentally validated through motion observations and demonstrated by grasping objects of various shapes.</p>