Upon moving into the run-down Spiderwick Estate with their mother, twin brothers Jared and Simon Grace, along with their sister Mallory, find themselves pulled into an alternate world full of faeries and other creatures.
| Actor | Role |
|---|---|
 Freddie HighmoreJared Grace / Simon Grace | Jared Grace / Simon Grace |
 Sarah BolgerMallory Grace | Mallory Grace |
 David StrathairnArthur Spiderwick | Arthur Spiderwick |
 Mary-Louise ParkerHelen Grace | Helen Grace |
 Nick NolteMulgarath | Mulgarath |
 Joan PlowrightAunt Lucinda Spiderwick | Aunt Lucinda Spiderwick |
 Andrew McCarthyRichard Grace | Richard Grace |
 Seth RogenHogsqueal (voice) | Hogsqueal (voice) |
 Martin ShortThimbletack (voice) | Thimbletack (voice) |
 Jordy BenattarYoung Lucinda Spiderwick | Young Lucinda Spiderwick |
| LLise Durocher-ViensMrs. Spiderwick | Mrs. Spiderwick |
 Tod FennellHelen's Co-Worker | Helen's Co-Worker |
 Mariah IngerNurse | Nurse |
| JJeremy LavalleyTow Truck Driver | Tow Truck Driver |
| KKyle SwitzerAdditional Performer | Additional Performer |
 Tyler Patrick JonesAdditional Performer | Additional Performer |
 Ron PerlmanRed Cap (voice) (uncredited) | Red Cap (voice) (uncredited) |