The award-winning Game of Thrones star was confirmed as the movie's newest cast member by director Bryan Singer.
"Officially like to welcome #PeterDinklage from #GameOfThrones to #XMEN #DaysofFuturePast Very very excited!" Singer said on his official Twitter account on Thursday morning (February 14).
Singer has not yet confirmed who Dinklage will play.
It was recently claimed that Days of Future Past will be set primarily in 1973, over ten years after the events of X-Men: First Class.
The new movie will see Sir Patrick Stewart, Sir Ian McKellen, Hugh Jackman, Anna Paquin, Ellen Page and Shawn Ashmore return to the series.
X-Men: First Class cast members James McAvoy, Michael Fassbender, Nicholas Hoult and Jennifer Lawrence are also tipped to return.
X-Men: Days of Future Past is due to debut on July 18, 2014.
Watch Michael Fassbender talking to Digital Spy about the X-Men: First Class sequel below: