A marine vessel door system implemented within or on a marine vessel gunwale, wherein the door can be easily opened to allow easy loading or unloading of passengers and cargo and closed in order to prevent passengers and cargo from entering or exiting the vessel. The marine vessel door system includes a door body and a door-moving mechanism which translates the door body frontward and rearward aligned to the marine vessel gunwale. The door-moving mechanism can include an articulated parallelogram attached to a fixed structure of the marine vessel and carrying the door body such that the door body translates forward and rearward jointly with a movable part of the articulated parallelogram.