As a secret agent suffering from amnesia, players unravel clues behind their true identity, while uncovering sinister plots against themselves, the U.S. government, and the recently assassinated U.S. president. XIII features the deepest story line of any first-person shooter, and players will be immersed in the game's graphic-novel world as they decide who is friend and foe in the ultimate government conspiracy. The game's cel-shaded graphics showcase its unique visual style, which pays homage to its comic roots. XIII also features a variety of exciting gameplay modes, including stealth, all-out action, collaborative gameplay, and innovative multiplayer modes.

XIII is the first online first-person shooter for the PlayStation 2 system, and is also online for Xbox Live and the PC. The game features several innovative multiplayer modes in addition to classic Deathmatch, Team Deathmatch, and Capture the Flag modes for the PC version. The Power Up mode is a custom Deathmatch multiplayer mode exclusive to the PlayStation 2 system, and includes unique pick-ups, including "invincibility" and "invisibility." In the Hunt mode, players chase a running target throughout the map, gaining points by hitting the target. Sabotage is a team multiplayer mode exclusive to Xbox, where two teams compete to take control of different strategic points in the map. Players are able to compete against up to 16 players over LAN and eight players via the Internet. In addition to featuring these innovative multiplayer modes, the PC version also includes an exclusive map editor.