Freddie Highmore

Jared Grace / Simon Grace

Sarah Bolger

Mallory Grace

David Strathairn

Arthur Spiderwick

Mary-Louise Parker

Helen Grace

Nick Nolte

Mulgarath

Joan Plowright

Aunt Lucinda Spiderwick

Andrew McCarthy

Richard Grace

Seth Rogen

Hogsqueal (voice)

Martin Short

Thimbletack (voice)

Jordy Benattar

Young Lucinda Spiderwick

Lise Durocher-Viens

Mrs. Spiderwick

Tod Fennell

Helen's Co-Worker