Firth will play William Weatherall Wilkins, president of Fidelity Fiduciary Bank.
The movie also stars Meryl Streep as Poppins’ cousin. Blunt will be playing the title character, with “Hamilton” star Miranda portraying a street lamplighter named Jack.
The film will be directed by Rob Marshall and produced by Marshall, John DeLuca, and Marc Platt.
The screenplay will be written by Oscar nominee David Magee based on “The Mary Poppins Stories” by P.L. Travers. Marc Shaiman composing an all-new score and Shaiman and Scott Wittman writing original songs
“Mary Poppins Returns” will hit theaters on Dec. 25, 2018.
Firth has had a busy year with “Genius” and “Bridget Jones’s Baby” bowing months apart. He is also a producer on the critically acclaimed drama “Loving.” He can be seen next reprising his role of Harry Hart in “Kingsman: The Golden Circle.”
Firth is repped by CAA and Independent Talent Group.