After the events of Just Cause 3, Rico Rodríguez is approached by Mira Morales, a native of Solís, who says that Rico's father, Miguel Rodríguez, was working on the Illapa Project, a weather weapon that Oscar Espinosa is using to control the people of Solís. After a failed attempt at deposing Espinosa and a run-in with his private army, the Black Hand, which is led by Mira's cousin Gabriela Morales, Rico forms an army of his own with Mira, named the 'Army of Chaos', aimed at taking down Project Illapa and ending Espinosa's regime.
The game takes place in the fictional nation of Solís, a large open world consisting of different biomes including snowy mountains and deserts. Rico can travel the game's world using his wingsuit and grappling hook, whose functions are expanded to include the ability to attach hot air balloons and rocket boosters on objects. A new wind and particle system was introduced, and it affects Rico's traversal with his wingsuit. The game also features a weather system and environmental hazards such as tornados and thunderstorms.