Harrington, who is currently performing in the Shakespeare’s Globe productions of Twelfth Night and Richard III on Broadway, will make his debut as Mr. Wormwood March 4.
Sieber, who will play 54 Below Feb. 4 and 11, will make his debut as Miss Trunchbull March 18.
They join a principal cast that also features Karen Aldridge as Mrs. Phelps, Lesli Margherita as Mrs. Wormwood, Jill Paice as Miss Honey and the four girls sharing the title role: Paige Brady, Gabriella Pizzolo, Ripley Sobo and Ava Ulloa.
Matilda The Musical, produced by The Royal Shakespeare Company and The Dodgers, opened in April 2013 at Broadway’s Shubert Theatre (225 West 44th Street). The production received four Tony Awards and a Tony Honor for Excellence in the Theater for each of the four girls who shared the title role, two Outer Critics Circle Awards, five Drama Desk Awards including Best Musical, and the New York Drama Critics Circle Award for Best Musical.