Soft continuum robots have many applications such as medical surgeries, service industries, rescue tasks, and underwater exploration. Flexibility and good accessibility of such robots are the key reasons for their popularity. However, the complexity of their structural design and control systems limit their broader applications. In this paper, a novel variable stiffness soft continuum robot based on pre-charged air, particle jamming, and origami is proposed. The robot is a bellow-like origami structure with internal chambers. A spine-like chamber is filled with particles, and three identical chambers surrounding the spine chamber are filled with pressurized air. When the origami structure is compressed, the particles are jammed by the compression force and the increased pressure of the three air chambers, thus increasing the overall stiffness of the robot. The robot expansion-contraction and bending are controlled by three tendons. An analytical model of the proposed stiffness variation mechanism has been developed. The effects of various parameters on the lateral and axial stiffness of the soft continuum robot have been investigated by experimental studies. A prototype robot has been fabricated to demonstrate grasping operations.