The second season of the American surrealist superhero thriller television series Legion premiered in Los Angeles on April 2, 2019, ahead of airing on FX from April 3 to June 12, totaling eleven episodes. The series is based on the Marvel Comics character David Haller, a mutant diagnosed with schizophrenia at a young age, who learns that his illness may actually be powerful psychic abilities. In the season, David and his friends join a government agency to find and stop the parasitic Shadow King before he finds his original body after being forced out of David's mind in the previous season. It was produced by FX Productions in association with Marvel Television, with Noah Hawley serving as showrunner.

Dan Stevens stars as David, with Rachel Keller, Aubrey Plaza, Bill Irwin, Jeremie Harris, Amber Midthunder and Jean Smart also returning from the first season to star. They are joined by Jemaine Clement and Hamish Linklater, promoted from guest roles in the first season, and Navid Negahban. The second season was ordered by FX in March 2017, with filming for the season relocating from Vancouver to California, to take advantage of tax incentives. Production began in September 2017, with practical effects again a priority for the series' crew.

The season received positive reviews from critics, who praised its performances, visual style, exploration of certain themes, and ambition, though some criticized it as prioritizing style over substance, and the finale garnered a polarized response. On June 1, Legion was renewed for a third and final season.

In June 2016, FX President John Landgraf said that Legion, if successful, could run for as many seasons as Hawley feels it needs to tell the story. In January 2017, Hawley said he was open to continuing the story past the first season, but didn't want the audience to get to the end of the first run and have "no resolution of any kind at the end of it." Star Dan Stevens said, "I know for a fact that there are more issues that David has to deal with than the one that we really address in the first season." FX renewed Legion for a second season on March 15, 2017. At the end of that month, Hawley explained that he planned for the season to have ten episodes, and to focus more on the series' other characters in addition to David Haller. He added, "I do tend to think that that's important, that even though the show isn't an anthology like Fargo, each season has a self-contained-ness to it, an identity to it. But I think it's a little too early to talk about what that identity might be." The season order was later expanded to eleven episodes, as announced by FX in May.

Hawley noted that the first season was about Haller's internal struggle against the Shadow King, and that the latter's transference to the character Oliver Bird at the end of the season signified a change to an external struggle for Haller that this season would explore. Hawley wanted to avoid having a villain-of-the-year structure, with the second season introducing a new antagonist, instead wanting to continue the story surrounding the Shadow King from his introduction in the first season that "makes for a potential showdown that we're really invested in as an audience". Hawley added that with the Shadow King reveal at the end of the first season, Haller can now blame "every bad thing he's ever done on the entity that's now gone, and now is thinking, 'I'm just a purely good person'... there's sort of a hubris to that." Stevens said that "we haven't even really scratched the surface of the number of characters or entities that are contained within [Haller]. The Shadow King was obviously one of them, and a large part, but there's a lot more going on." Hawley did not have a plan for the second season when he ended the first on a cliffhanger, and enjoyed the challenge of developing the story from that point, noting that this was the first "true" second season he has created. Hawley did not have to repeat this at the end of the second season, as he had a plan for future seasons by that point.

The second season begins a year after the end of the first, with Hawley feeling the time jump allowed them to "muddy the waters" rather than be "all clarity all the time", since "that's the fun of the show, the mystery of trying to figure things out." Stevens added that "everybody's going to be playing catchup", including the audience and Haller. Hawley also said that the season would explore the world of heroes and villains, and that it was not yet decided which direction Haller would go. The season spends more time inside the minds of the characters and in the Astral Plane than the first, and also explores "more specific genres and storytelling moments" to both be more ambitious than the first season and not repeat what had been done before; Hawley wanted to "use the genre to solve the characters ... to explore the characters and stories that you couldn't in a straight drama". The main story of the season focuses on Farouk searching for his original body, since mutant abilities are genetic and being reunited with the body will make him even more powerful. The season includes some episodes that Hawley considered "more stand-alone", that are still relevant to the plot of the season but were less interested in the plot and more character-focused. This was something Hawley had not been comfortable doing during the first season due to introducing the "different than everything else"-series to audiences then.

To avoid the season becoming "a good versus evil or white hat versus black hat situation", Hawley wanted to focus on thematic ideas such as "our shared reality being a choice that we make. Sometimes societies go a little bit crazy. How does that happen?" To help explore that idea, Hawley created an "educational segment" which he soon decided to add to each episode of the season. The segments are narrated, and are intended to "take these concepts of mental illness, and visualizing them in a way where you can tell a story."

Returning from the first season to star are Stevens as David Haller, Rachel Keller as Sydney "Syd" Barrett, Aubrey Plaza as Lenny Busker, Bill Irwin as Cary Loudermilk, Jeremie Harris as Ptonomy Wallace, Amber Midthunder as Kerry Loudermilk, and Jean Smart as Melanie Bird. Hawley considered Barrett to be the co-protagonist of the season alongside Haller, calling it a "two-hander", with the season further exploring their relationship and comparing it to that of Melanie Bird and her husband Oliver. Hamish Linklater joins the main cast, having portrayed Clark Debussy in a guest role in the first season.