Set in the 17th century Caribbean, Port Royale 3 is a business simulation game, similar to the Patrician series. The player assumes the role of an independent captain amidst the kingdoms of Spain, England, France and the Netherlands, and independent factions of pirates, fighting over the New World colonies. The player is not limited to a single allegiance; the fluid diplomacy allows the player to build alliances and rivalries throughout the game.
There are two "career paths": Adventurer, which focuses on combat and conquest; and Trader, which focuses on setting up trade routes and city building. Although the player is free to pursue activities from both of these modes in the same game, the single-player story mode is divided into two distinct campaigns that focus around the two career paths.
Unlike the previous two games in the series, Port Royale and Port Royale 2, Port Royale 3 offers a multiplayer mode allowing up to 4 players to battle for control of the seas.