Throughout the series, several major character shifts and dramatic twists unfold:
- Season 1: Buck Spivey's accidental shooting of unarmed teen Raymont Harris leads to Commander Hicks promoting Hondo over senior officer Deacon. Hondo's secret romance with Captain Jessica Cortez creates internal friction before she exits to take an FBI post.
- Seasons 2–3: Jim Street faces betrayal when his imprisoned mother, Karen, is released and drags him into criminal dilemmas. Luca deals with hip complications threatening his field eligibility.
- Season 4: After white supremacist infiltration in the department is uncovered, Hondo goes on record with the press to expose racism within law enforcement, resulting in Hicks stripping him of his squad leader rank.
- Season 5: Hondo retreats to Mexico, dismantles local criminal rings, and returns to LA where he is reinstated as Twenty Squad leader. Chris Alonso retires from SWAT to take over Mama Pina's safe house for undocumented immigrant women, solidifying her long-term romantic relationship with Street.
- Seasons 6–7: Street departs to lead the Long Beach SWAT unit. Luca is shot during a robbery intervention, suffering permanent nerve damage that forces him into medical retirement. Hondo marries Nichelle and builds a family life.
- Season 8 & Series Finale ("Return to Base"): Ex-Russian mercenary leader Dmitri Rykov plants citywide explosives to blackmail the city. When Rykov is held at SWAT HQ, his mercenary faction launches a massive armed siege on the facility. Twenty Squad successfully defends the building and neutralizes the assault. Deacon, having earned financial security from his private security venture, gifts custom watches to Hondo, Tan, Powell, Alfaro, and Gamble. The series concludes with a new emergency call rolling in, Hondo rallying the team with "What are we waiting for? Gear up. Let's go save this city," and each officer touching the SWAT logo on the wall as they head into action.