FX's Legion will end after its upcoming third season. At the Television Critics Association winter press tour, FX Networks CEO John Landgraf said (via Variety) that showrunner Noah Hawley always projected the series to only last three seasons, and that the ending will be a natural conclusion.
This comes as the impending Walt Disney Company acquisition of 21st Century Fox (and the X-Men TV/film rights, which would include Legion) comes to an expected close. FX (but not its sister station Fox) is part of the assets being acquired by Disney.
Legion's third season is expected to debut later this year.