Turner, 18, became a household name with her portrayal of Sansa Stark in 'Thrones'.
The casting news was confirmed by director Bryan Singer on Twitter.
Alexandra Shipp and Tye Sheridan have also joined the movie as Storm and Cyclops.
James McAvoy, Michael Fassbender, Nicholas Hoult, Jennifer Lawrence and Evan Peters will all reprise their roles in the next instalment of the franchise where, Oscar Isaac will play the supervillain Apocalypse.