Watch Dogs: Legion is an action-adventure game played from a third-person perspective. The game is set within an open world, fictionalised representation of near future London, which will encompass notable landmarks, boroughs, and cultural styles of the city. The game's setting takes place within a London that has become a surveillance state. Personal liberties have been vastly limited, and citizens are constantly monitored in their activities by Albion, a private security company that acts as the city's law enforcement. The player will have the ability to navigate the city either by foot, using vehicles, or fast-traveling via the city's Underground stations. Unlike the previous games in the series which focused on the use of a single protagonist to drive the story's narrative, Legion features the ability to control multiple characters within the game's setting. Each of these characters can be recruited through a unique mission, though this depends on their standing with DedSec; for example, a character who the hacker group helps out will be in favour of aiding them when asked and completing their recruitment mission, whereas a character whose family member was accidentally killed by a DedSec member will not tolerate the group and likely refuse to join. Once a character is recruited into the player's roster, they are assigned to one of three classes: combat, stealth or hacking. Each class features its own set of tools and ability upgrades when a character levels up from completing missions and activities. Each character also has their own background which dictates a special skill or trait they have. For example, a recruited character may be more skilled with drones and thus can do more damage with them, while another is an "adrenaline junkie" who deals more damage but at the possible risk of dying at any random moment. All characters in the game recruited into the player's roster have their own personal lives when not being controlled, can be fully customised with various clothing options, and can wield a mixture of lethal and non-lethal weapons, the latter featuring a more extensive selection than in previous titles. Although the player can recruit a large roster of characters to control, each can be permanently lost during the course of a playthrough. Characters risk the possibility of being killed either while conducting operations for DedSec against other groups or against local law enforcement; in such cases where the currently controlled character is critically injured, players can choose to either make them surrender to their opponents and allow them to be rescued by another character, or attempt to resist and lose their pursuers at the risk of being killed in action and being permanently removed from the player's roster of playable characters, thus forcing the player to switch to another character. Players can also join a team of up to four players in cooperative gameplay, sharing progression between single-player and multiplayer modes.
Watch Dogs: Legion is being developed by Ubisoft Toronto, with additional work being provided by sister studios Ubisoft Montreal, Ubisoft Paris, Ubisoft Bucharest, Ubisoft Kyiv and Ubisoft Reflections. The development team is headed by creative director Clint Hocking, who was recruited to assist on the game's creation due to Ubisoft moving development from their studio in Montreal to Toronto, and recruiting developers who had previously worked with him on Far Cry and Far Cry 2. Upon its reveal at E3 2019, many outlets described the futuristic London setting as post-Brexit, what could potentially happen following the expected departure of the United Kingdom from the European Union. This choice of setting became a point of debate in the media, as there are several political questions related to post-Brexit. Hocking stated that they had come onto the idea of this setting around a year and a half before the actual Brexit vote in 2016, and that while the game does involve Brexit, the intent was not to try to debate the nature of Brexit, but to show and debate elements already existing in the world today that lead to events such as Brexit. On 25 January 2020, Hocking pointed out that, as a "creator of culture", the aim of including real-world elements such as Brexit is to provide a means of engagement for players about the world around them, though with the development team taking considerable thought on how to implement these and other events occurring in the real-world within Legions setting.
Watch Dogs: Legion was teased by Ubisoft via Twitter on 5 June 2019, before its announcement at E3 2019. The game was initially scheduled for release on 6 March 2020, where the PC versions of the game would be exclusive to the Epic Games Store for as long as a year, but by October 2019 the game had been delayed into Ubisoft's 2021 fiscal year. During the July 2020 "Ubisoft Forward" event, Ubisoft announced the game's planned release on 29 October 2020, for Microsoft Windows, PlayStation 4, Xbox One, and Stadia, with PlayStation 5 and Xbox Series X versions to arrive later in 2020. In January 2020, BBC reporter Marc Cieslak conducted an interview with Hocking about the game for Click, which in a world's first, involved using the studio's motion capture software to allow it to take place within the virtual setting of the game.