• 
  Jude Law

  Charles (voice)
• 
  Susan Sarandon

  Aunt Agatha (voice)
• 
  Stephen Fry

  Headmaster (voice)
• 
  Jason Schwartzman

  Arcangelo Corelli (voice)
• 
  John DiMaggio

  Various Voices (voice)
• 
  Peter Serafinowicz

  Various Voices (voice)
• 
  Jaden Smith

  Kaz Kaan (voice)
• 
  Richard Ayoade

  Various Voices (voice)

• 
  Nico Muhly

  Professor Muhly (voice)
• 
  Kiernan Shipka

  Helenist (voice)
• 
  Willow Smith

  Helenist (voice)
• 
  Tavi Gevinson

  Helena St. Tessero (voice)
• 
  Amandla Stenberg

  Helenist (voice)
• 
  The Kid Mero

  Lexy (voice)
• 
  Desus Nice

  Gottlieb (voice)