Els has previously appeared on stage in Timon of Athens, Antigone and The Cherry Orchard at the National Theatre and on screen in Ripper Street, The Bletchley Circle and Call The Midwife.
His other theatre credits include Mamma Mia! (Novello), Oklahoma! (Chichester Festival Theatre), The New Yorkers (Sadler's Wells), Never Forget (West End and Tour) and Spamalot (West End).
Also joining the cast in September will be the aptly named Matilda Shapland and Violet Tucker, who will join Tasha Chapple and Lottie Sicilia in the title role.
The show, adapted from Roald Dahl's perennially popular book about a bookish young girl with magical powers, receives its Australian premiere at Sydney's Lyric Theatre in August next year.
The current West End cast also includes: Lucy Jane Adcock, Fabian Aloise, Ashley Cooper, Jonathan Cordin, Ashleigh Drew, Nicholas Duncan, Demi Goodman, William Kenning, Antony Lawrence, Max Parker, Lisa Davina Phillip, Charlotte Scott, Tommy Sherlock, Hollie Taylor, Amy Thornton, Jason Winter and Joshua Wyatt.
Lara Denning will play the role of Miss Honey from 29 September to 26 October.
The production is designed by Rob Howell, with choreography by Peter Darling, orchestrations, additional music and musical supervision by Christopher Nightingale, lighting by Hugh Vanstone, sound by Simon Baker and the special effects and illusions are by Paul Kieve.
Video: Watch Minchin and Kelly interview their new Miss Trunchbull: