The actress joins Logan Lerman and Brandon T. Jackson in the fantasy-adventure movie being directed by Chris Columbus. Columbus and Craig Titley have adapted the screenplay from Rick Riordan's best-selling children's novel.
The Greek mythology-inflected book involves Poseidon's half-human son, Percy, who's on a quest across modern America to prevent a war among the gods.
Daddario will play Athena's 18-year-old daughter, Annabeth, a warrior at Camp Half-Blood with Percy and potential romantic foil.
"Lightning Thief" is the first of five novels about Percy Jackson and the Olympians -- the fifth, "The Last Olympian," is due in stores in May.