The team evaluated the core of the Rainbow Six franchise and believed that letting players impersonate the top counter-terrorist operatives around the world suited the game most.

[8] Teamwork and cooperation are encouraged in Siege, and players need to take advantage of their different abilities in order to complete the objective and defeat the enemy team.

[12] In addition to destruction, players on the defending team can also set up a limited number of heavy-duty fortifications on walls and deployable shields around them for protection; these can be destroyed through breaching devices, explosives, or by utilizing operator specific gadgets in the case of the former.

[16] Vertical space is a key gameplay element in the game's maps: players can destroy ceilings and floors using breach charges and can ambush enemies by rappelling through windows.

Recruits go through multiple exercises to prepare them for future encounters with the White Masks, training to perform hostage rescue and bomb disposal.

Eventually, the White Masks launch a chemical attack on Bartlett University, and the recruits are sent to disarm the bombs and eliminate the enemy presence.

In 2019, Arnot resigns from her position to become the Secretary of State and recommends her advisor, Doctor Harishva "Harry" Pandey (Andy McQueen), to take her place as "Six".

Some time later, Harry invites members of a private military company, Nighthaven, to join Team Rainbow, in order to observe their skills and prevent competitors from also hiring them.

Following the assassination of a high-profile tech company CEO, Masayuki Yahata, Team Rainbow investigates his death and finds evidence implicating Nighthaven's involvement.

Rainbow members Gustave "Doc" Kateb (Alex Ivanovici), Elena "Mira" Álvarez (Anahi Bustillos), Julien "Rook" Nizan (Marc-André Brunet) and Sam "Zero" Fisher (Jeff Teravainen) confront Deimos and apprehend him.

Skopós teams up with Rainbow operative Grace "Dokkaebi" Nam (Christine Lee) to assault a Keres safehouse and retrieve intel pertaining to the organization.

[36] According to Alexandre Remy, the brand director, the team was confident in their new vision for the game but very nervous when they revealed it, realizing the change of direction would likely disappoint some fans.

The team also consulted counter-terrorism units, such as the National Gendarmerie Intervention Group (GIGN), for their opinions on how they would react during a hostage rescue situation.

[46] The destruction mechanic prompted Ubisoft to change their level-design approach, as they had to ensure that the level was still logical and realistic when parts of the environment were destroyed.

They concluded that the respawn system worked to the benefit of strong players and placed individual skill above teamwork,[48] which did not fit the developer's focus on game tactics.

Removing the respawn feature meant greater consequences for taking risks, and players had to rely on their teammates in order to survive and achieve objectives.

[57] A closed alpha-testing was held by Ubisoft on April 7–13, 2015, in which players could play an early version of the game in order to help the development team test their servers and core gameplay loops, and to provide feedback.

[76] Downloadable content for the game was divided into several seasons, with a Mid-Season Reinforcement patch which added new weapons and modified some of the operators' core abilities.

[84] ESL and Ubisoft officially announced Tom Clancy's Rainbow Six Pro League, a global tournament for Windows and Xbox One players.

[91][92] The Six Invitational 2020, in February 2020, had the highest prize pool in all of Rainbow Six with $3,000,000 split among 16 teams, with the victors, Spacestation Gaming from North America, taking home the lion's share of $1,000,000.

Chris Carter from Destructoid praised the game's open-ended nature, which made each match unpredictable and helped the experience to stay fresh even after an extended period of playing.

[107] James Davenport from PC Gamer echoed this thought, and he described Siege as a "psychological race" in which players are constantly trying to outwit their opponents.

[112] The "No Respawn" system was praised by Butterworth for making each match feel intense, as even the best player needs to think tactically in order to win.

Butterworth described it as a "surprisingly robust" mode and thought that there were great tutorial missions that help players to understand gameplay before trying multiplayer.

[117][118] In May 2015, CEO of Ubisoft Yves Guillemot announced that the company expected the game to outsell Far Cry 4's seven million sales over the course of its lifetime because of post-launch support.

[34] Jeff Grubb from VentureBeat attributed Siege's high player retention rate and successful eSports events to Ubisoft's continuous and frequent updates to the game.

[135] GameSpot described Siege as "one of modern AAA gaming's biggest comebacks", and the best proof to show that the "games-as-a-service" model works well, attributing its success to Ubisoft's continuous updates and the thriving community.

Unlike titles such as Star Wars Battlefront II (2017), the game's monetization methods and the use of loot boxes generated minimal amount of backlash from players.

Future Ubisoft multiplayer-focused titles – such as For Honor – adopted this structure, in which the company would provide free DLC and updates several years after the game's official release.

[138] On November 2, 2018, Ubisoft Montreal announced they were going to make "aesthetic changes" to Tom Clancy's Rainbow Six Siege by removing references to death, sex, and gambling in order to comply with regulations of Asian countries.