We met David [Dan Stevens] who had been at his lowest point and tried to kill himself, then he meets Syd [Rachel Keller] and he gets balanced out.

[14][15] Returning from previous seasons to star are Dan Stevens as David Haller, Rachel Keller as Sydney "Syd" Barrett, Aubrey Plaza as Lenny Busker, Bill Irwin as Cary Loudermilk, Navid Negahban as Amahl Farouk / Shadow King, Jeremie Harris as Ptonomy Wallace, Amber Midthunder as Kerry Loudermilk, and Hamish Linklater as Clark Debussy.

[9] In January 2019, Lauren Tsai was cast as Switch, "a young mutant whose secret ability serves as the key to executing David Haller's plan".

[10] In February, it was announced that the characters Gabrielle Haller and Professor X would appear played by Stephanie Corneliussen and Harry Lloyd, respectively.

[11] Jean Smart and Jemaine Clement also return in special guest roles as Melanie and Oliver Bird in "Chapter 25".

Reinforced by the idea of David leading a cult, inspirations for set design as well as clothing were drawn from psychedelic visuals from the 1960s and 70s, all while integrating with modern-day elements to avoid dating the series.

A soundtrack album for the season featuring Russo's score and reimagined covers was released digitally on December 18, 2020.

All music by Jeff Russo, except where noted:[19] The season began airing on FX on June 24, 2019, and consists of eight episodes.

The website's critical consensus reads, "In its final season, Legion remains a singular piece of visually arresting, mind-bending television that never fails to surprise.

"[20] Metacritic, which uses a weighted average, assigned a score of 72 out of 100 based on six critics, indicating "generally favorable reviews".