After defeating all rivals in Stilwater, the Saints transformed into a media empire by merging with Ultor Corporation and expanded their street gang's influence. However, when a fellow actor tries to "research" his role for the Saints' movie, the Saints rob a bank and get caught. The Syndicate bribes the police, gets the Saints' leader Gat and Shaundi released, and forces them to negotiate business with Phillipe Loren. When they refuse, a gunfight ensues, resulting in Gat's escape and presumed death.
The Saints relocate to Steelport, a city once known for its factories but now struggling due to economic failure. The Syndicate controls the city through three gangs: The Morningstar, led by DeWynter sisters and Loren, The Luchadores controlled by Mexican wrestler Killbane, and The Deckers led by Matt Miller and his group of computer geniuses. The Saints aim to take control over the city, fighting other gangs and reclaiming their former glory.
Saints Row: The Third is the third main game in the sandbox shooting and driving series, focusing on third-person action, free-roaming driving, and urban warfare. The protagonist explores Steelport, performs missions to advance the story, and participates in side activities such as Activities, Strongholds, and Flashpoints.
Completing missions earns money, weapons, cars, and gang reputation. While Saints Row games used reputation for new missions, The Third uses it as experience points to upgrade weapons and cars. Money can be used to customize the gang's appearance, outfits, and headquarters, or purchase shops and properties in Steelport. The Initiation Station system allows players to share their characters with others.
New novelty weapons are introduced, alongside traditional armaments. Players can call down airstrikes on enemy camps or control vehicles using a remote electric bug. Unlike previous games, there's no health recovery; instead, health regenerates faster out of combat. Almost every action in the game can be sped up by holding down a special button.
The game features co-op mode, where the second player participates in all missions and activities, receiving credit for completion. Some activities have different rules when played with two players. Co-op requires a single-use online pass, and there's no competitive multiplayer mode.