Just Cause 3 is the third main game in the action series set in an open world environment with a focus on shooting, causing destruction and over-the-top violence and stunts. The protagonist is once again the Mexican Rico Rodriguez. Set six years after the events of the previous game, Rico returns to Medici, the fictional Mediterranean island where he grew up until dictator General Sebastiano Di Ravello took control. The main story sees him team up with the scientist Dimah al-Masri and his former childhood friend Mario Frigo. They work for the rebellion who seek to overthrow Di Ravello and thwart his plans to take over the entire world. At first however, Rico needs to sabotage many operations and help to establish the rebellion's influence, before the dictator can be taken on. Agent Sheldon from the previous game also returns.

As in the previous games Rico is in most situations able to do everything himself. Instead of following the main missions the islands can be explored without limits right away. The environment is now an archipel rather than a single island. Medici is divided into several regions, then further into provinces and even further into settlements. To liberate an entire province all settlements need to be freed. This is usually done by taking over (i.e. blowing up) a command center, which is usually a large army base with heavy forces. There are also other activities to free a settlement, such as taking down billboards or statues, disabling propaganda messages or taking over the local police station. When all required activities are completed, the rebel flag is raised and the settlement has been taken over. Afterwards these can also be used for fast travel.

Rico can use any vehicle in the game such as cars, but also tanks, ships, fighter jets and attack choppers. After unlocking them, he can call in rebel supply drops to have a certain vehicle delivered. In some cases the AI adapts the difficulty level to match the chosen vehicle. Drops can also be used for weapons and equipment. There is no in-game currency. Important returning elements are the parachute to dive down and the grappling hook to quickly move through the environment or hitch rides. Many vehicles can be customized and be used as weapons, next to regular ranged weapons such as machine guns, rifles and missile launchers. Unlike the previous game C4 is now always available and with an infinite supply, but only five can be used simultaneously. Entirely new is the wingsuit as a means of transportation. The hook is also used to hook two items or vehicles, and then the cable is decreased to bring them together, often causing havoc. There are many upgrades to unlock, for instance making the hook much more effective and allowing more at a single time. Almost any action is recorded in online leaderboards for worldwide comparisons. There are also many challenges that encourage the player to experiment through mini-games and races.