Torsional actuators are a class of artificial muscle technology that generates torque and produces rotary motion in response to various stimuli. This paper presents a novel torsional actuator combining an origami-inspired twisting skeleton and an artificial muscle. The process of torsional actuator design starts from identifying a foldable twisting skeleton which is capable of achieving helical motion thereby translating linear motion to rotational motion. This is followed by the integration of an artificial muscle to drive the twisting skeleton. Kinematics of both the twisting skeleton and artificial muscle are analyzed. Following the design and kinematic analysis, a prototype is developed by bonding 3D printed polylactic acid (PLA) parts and thermoplastic polyurethane (TPU) films to form the twisting skeleton and laminating TPU membranes by using heat sealing tools to form the artificial muscle. A pneumatic control system is built to evaluate the performances of torsional actuator by testing the relationship between twisting angle, air pressure, driving force and output torque. Experimental results show that the relationship between air pressure, driving force and output torque is proportional at a given twisting angle. The novel torsional actuator augmenting an origami-inspired skeleton and soft artificial muscle leads to simplified analytical model and has potential of driving robotic systems in environment where pneumatically actuated systems are preferred over electrical machines and drives.