"I was waiting until it was official. It's official!" Miranda tweeted alongside an emoji of Poppins' signature umbrella.
Miranda's musical Hamilton is currently the toast of Broadway, recently earning a record-setting 16 Tony Award nominations. Blunt can now be seen in The Huntsman: Winter's War.
Walt Disney's battle to convince Mary Poppins author P.L. Travers to allow him to adapt her beloved fantasy novel for the big screen was the subject of the 2013 Tom Hanks-Emma Thompson movie Saving Mr. Banks.