A big screen adaption of the hit Broadway and West End musical is currently scheduled for release in 2021.
The film has been in the works for many years and now the musical's composer Schwartz has given an update on progress.
In a chat with The Hollywood Reporter, he said the script was still being worked on “but the process is heating up” with talk about casting starting.
Schwartz revealed his excitement at modifying the stage show for the screen, saying he was looking forward "to be able to do things that we thought about when we were doing the show, but of course we couldn't do.
"And it's been wonderful for my collaboration...Winnie Holzman [the musical's book writer] and myself to be back in that world and back with those characters we love and think about 'How do you tell that story as a movie?'”
Stephen Daldry will direct the film and has been meeting with production designers, the publication adds.
Schwartz previously revealed the screen adaption would see new songs as well as other changes to the current stage version.
He told Variety in a 2017 interview: "In order to do something that will work on its own merits, you have to do something different.
"The only concern is people who would be coming expecting to see a filmed version of the play. They’re not going to see that."
One of the world's biggest musicals, Wicked has been running at London's Apollo Victoria Theatre for 13 years - and recently extended until May 2020.
The magical tale reveals the 'true untold story' behind the Wizard Of Oz and just what happened before Dorothy dropped in. Featuring some of musical theatre's most iconic songs, such as Defying Gravity and Popular, Wicked will send your spirits soaring to heights you’ll never forget.