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)