Sophie Nélisse as Gilly Hopkins

Kathy Bates as Maime Trotter

Glenn Close as Nonnie Hopkins

Bill Cobbs as Mr Randolph

Octavia Spencer as Miss Harris

Julia Stiles as Courtney Rutherford Hopkins

Clare Foley as Agnes

Billy Magnussen as Ellis

Zachary Hernandez as W.E.

Sammy Pignalosa as Rajeem

Toby Turner as Ticket Agent

Richard Topol as Principal Evans

Salvatore Rossi as Stevie

Cameron Clifford as Ed

Julee Cerda as Mrs. Hong

Johanna Day as Principal Maynard

Katherine Paterson as Clerk

Frank Oz as Cookie Monster (voice)

Blanca Camacho as Additional Voices (voice)

Gavin Westerlind as Ramirez

Sienna Stuebe as Neighbor

Athena Stuebe as Neighbor and Student

Loyzo as Neighbor

Liz Imperio as Neighbor

Connor Keegan Dosch as School student

Cynthia Basinet as Attendee

Cara Cooper as Woman with Book