Freddie Highmore as Jared Grace / Simon Grace

Sarah Bolger as Mallory Grace

David Strathairn as Arthur Spiderwick

Mary-Louise Parker as Helen Grace

Nick Nolte as Mulgarath

Joan Plowright as Aunt Lucinda Spiderwick

Andrew McCarthy as Richard Grace

Seth Rogen as Hogsqueal (voice)

Martin Short as Thimbletack (voice)

Jordy Benattar as Young Lucinda Spiderwick

Lise Durocher-Viens as Mrs. Spiderwick

Tod Fennell as Helen's Co-Worker

Mariah Inger as Nurse

Jeremy Lavalley as Tow Truck Driver

Kyle Switzer as Additional Performer

Tyler Patrick Jones as Additional Performer

Ron Perlman as Red Cap (voice) (uncredited)