Seth Grahame-Smith's novel is based on the Jane Austen classic, but features additional zombies.
According to Deadline, Freaks and Geeks writer Mike White dropped out before being replaced by Gillespie.
The original Pride and Prejudice, written at the end of the 18th century, is about the troubled courtship of Elizabeth Bennet and the proud Mr Darcy.
Gillespie is also currently at work on the remake of 1985 cult film Fright Night, which was directed by Tom Holland.
The new version, featuring David Tennant, will focus on the trials of a teenager who suspects that his next-door neighbour is a vampire.