The director tweeted the picture on Monday (May 20) and described her character as "vengeful".
The photo shows Jennifer Lawrence in a body suit as opposed to paint. Lawrence has previously said: "I'm so excited because I'm going to wear a body suit.
"It will be from neck down so it will cut out time and the blisters."
> Halle Berry as Storm: first look
She will rejoin X-Men: First Class cast members James McAvoy, Michael Fassbender and Nicholas Hoult in the film.
Singer has also secured the return of Hugh Jackman, Sir Ian McKellen, Halle Berry, Sir Patrick Stewart, Anna Paquin, Ellen Page and Shawn Ashmore from the previous trilogy.
Game of Thrones star Peter Dinklage will star as one of the film's villains.
X-Men: Days of Future Past will debut on July 18, 2014.
Watch Jennifer Lawrence preparing for the role of Mystique in X-Men: First Class below:
Photo gallery - Jennifer Lawrence's fast rise to fame in pictures: