Gaumond will play Miss Trunchbull, a role originated by Bertie Carvel, who is currently playing it on Broadway. Murphy will take on the role of Mrs Wormwood. Haley Flaherty will continue in the role of Miss Honey until 7 September 2014.
Alex Gaumond's stage credits include Top Hat The Musical (Aldywch Theatre), Jesus Christ Superstar (Ljubljana, Slovenia), We Will Rock You (Dominion Theatre / original UK tour) and Legally Blonde (Savoy Theatre).
The Royal Shakespeare Company's Matilda, which is based on Roald Dahl's classic children's novel, originally opened in Stratford-upon-Avon in 2010, and has won almost fifty awards to date.
The Broadway production won four accolades at the Tony Awards last night including Best Scenic Design of a Musical and Best Lighting Design of a Musical for Rob Howell and Hugh Vanstone.
Further casting for the London production is to be announced soon.