The high-wing twin-engine airplane was not damaged and a lineman was seriously injured when the lineman inadvertently walked into the turning propeller for the number 1 engine while undergoing ground operations prior to the night flight. The lineman, who was reported to have completed all required training, recently changed work shifts and collectively had a total of six-months of experience. It was also reported that normally aircrews remove their own wheel chocks. The pilot stated that as the airplane completed both engine starts, in preparation for flight, the employee quickly approached the airplane to unplug the ground power unit (GPU) when he preceded to cross beneath the left wing from forward-to-aft retrieving the left main landing gear wheel chocks. While recovering the left wheel chocks the linemen was struck by the left engine propeller blade sustaining serious injuries. The airplane was standing at the time of the mishap. The pilot-in-command then performed an engine shutdown, exited the aircraft and assisted the injured linemen. Weather at the airport was not a factor in the mishap.